0  D     L  I  D  K  M  K  I^^jTE 


NEWSPAPERS. 

Goods    and    Pap< 
Hangings, 


>*J^* 


ROLLO'S 


PHILOSOPHY. 


i  WATER.] 


THE  HOLLO  SERIES 


18    COMPOSED   OF    FOURTEEN   VOLUMES,  TIZ 


Rollo  Learning  to  Talk. 
Rollo  Learning  to  Read. 
Rollo  at  Work. 
Rollo  at  Play. 
Rollo  at  School. 
Rollo's  Vacation. 
Rollo's  Experiments. 


Reno's  Museum. 

Rollo 

Rollo 

Rollo 

Rollo 

Rollo 

Rollo 


s  Travels, 
a  Correspondence, 
s  Philosophy — Water. 
s  Philosophy — Air. 
e  Philosophy — Fire. 
8  Philosophy— Sky. 


A    NEW    EDITION,   REVISED   BY   THE   AUTHOR 


NEW   YORK: 
SHELDON   &  CO.,  115  NASSAU  STREET. 


1860. 


Entered,  accct itcg  tr  A»»  of  Con*r««. '  u  t^j  Year  1855,  bjr 

PHILL.li'S,  SAMTSO>f,  &   JO., 
fa  UM  Clerk't  Office  of  the  District  Court  of  the  District  of  UatsachoMt*  S 


PREFACE. 


THE  main  design  in  view,  in  the  discussions 
which  are  offered  to  the  juvenile  world,  under  the 
title  of  THE  ROLLO  PHILOSOPHY,  relates  rather  to 
their  effect  upon  the  little  reader's  habits  of  think- 
ing, reasoning,  and  observation,  than  to  the  ad- 
ditions they  may  make  to  his  stock  of  knowledge 
The  benefit  which  the  author  intends  that  the 
reader  shall  derive  from  them,  is  an  influence  on 
the  cast  of  his  intellectual  character,  which  is  re- 
ceiving its  permanent  form  during  the  years  to 
which  these  writings  are  adapted. 

The  acquisition  of  knowledge,  however,  though 
in  this  case  a  secondary,  is  by  no  means  an  unim- 
portant, object ;  and  the  discussion  of  the  several 
topics  proceeds  accordingly,  with  regularity,  upon 
a  certain  system  of  classification.  This  classifica- 
tion is  based  upon  the  more  obvious  external  prop- 
erties and  relations  of  matter,  and  less  jpon  those 
1* 


O  PREFACE. 

which,  though  they  are  more  extensive  and  gen« 
eral  in  their  nature,  and,  therefore,  more  suitable, 
in  a  strictly-scientific  point  of  view,  for  the  foun- 
dations of  a  system,  are  less  apparent,  and  require 
higher  powers  of  generalization  and  abstraction ; 
and  are,  therefore,  less  in  accordance  with  the. 
genius  and  spirit  of  the  Rollo  philosophy. 

As  teachers  have,  in  some  cases,  done  the 
author  the  honor  to  introduce  some  of  the  pre- 
ceding works  of  this  class  into  their  schools,  as 
reading  books,  &-c.,  considerable  reference  has 
been  had  to  this,  in  the  form  and  manner  of  the 
discussion,  and  questions  have  been  added  to  facil- 
itate the  use  of  the  books  in  cases  where  parents 
or  teachers  may  make  the  reading  of  them  a  regu- 
lar exercise  of  instruction. 


CONTENTS. 


CHAPTER    1.                            Pigft 
WATER,. 9 

CHAPTER   II. 
WATER, 26 

CHAPTER  1" 
THE  THREE  DIFFICULTIES, 42 

CHAPTER  IV. 
AVAPORATION, 54 

CHAPTER   V. 
DAM  BUILDING, 66 

CHAPTER  VI. 
HYDRAULICS, 83 

CHAPTER  VII. 
THE  MEASURE  OF  PRESSURE, 95 


CONTENTS. 


CHAPTER  VIII.  Page 

BLOWING, Ill 


CHAPTER  IX. 
BRIDGE  BUILDING, 133 

CHAPTER  X. 
MOMENTUM, 151 

CHAPTER  XL 
JONAS'  s  LECTURE, 163 

CHAPTER  Xll. 

182 


THE 


ROLLO    PHILOSOPHY. 


CHAPTER   I. 
WATER. 

IN  the  yard  behind  the  house  where  Rollo 
lived,  there  stood  a  pump,  with  a  sort  of 
trough  be'fore  it,  made  of  planks,  which  was 
intended  to  conduct  the  waste  water  into  a 
large  hole  in  the  ground  before  it.  Rollo 
often  wondered  where  the  water  came  from, 
which  was  brought  up  by  working  the  pump ; 
and,  also,  where  it  went  to,  down  in  the  hole 
at  the  end  of  the  trough.  He  looked  into 
the  nose  of  the  pump,  but  found  that  he 
could  see  in  but  a  very  little  way.  He 
also  put  his  head  down  close  to  the  hole. 
It  was  a  square  hole,  with  plank  sides.  It 
looked  quite  dark  down  there,  but  he  thought 
he  could  see  some  stones  at  the  bottom. 

The  trough  had  only  three  sides ;  the  part 
towards  the  hole  was  of  course  left  open, 


10  WATER. 

so  that  the  water  might  run  olF;  and  it 
was  placed  so  as  to  be  inclined  towards  the 
hole,  in  order  that  the  water  might  run  off 
more  rapidly.  Hollo  had  often  tried  to  stop 
the  water,  by  damming  it  up  with  stones ; 
but,  though  he  packed  the  stones  as  closely 
as  he  could,  it  would  leak  through,  almost 
as  fast  as  he  could  pump  it  in.  At  length 
Jonas,  the  boy  who  worked  at  his  father's, 
told  him  that  he  would  stop  the  water  for 
him.  So  he  took  a  measure,  and  measured  the 
breadth  of  the  side  that  was  left  open  ;  then  he 
went  to  the  barn,  and  took  a  handsaw,  and 
sawed  off  a  piece  of  board,  of  exactly  the 
right  length  to  stop  up  the  passage.  The 
sides  of  the  trough  sloped  towards  each  other 
a  little,  so  that  he  could  press  it  in  tight; 
when  it  was  fitted,  Jonas  pumped  away, 
for  some  time,  and  Hollo  was  delighted  to 
perceive  that  very  little  of  the  water  escaped. 
The  trough  was  soon  filled  with  water,  and 
it  made  Rollo  quite  a  little  pond. 

Jonas  looked  around  to  the  lower  side  of 
the  board,  and  observed  that  there  was  quite 
a  leak  there,  after  all.  "  However,"  said  he, 
"  I'll  calk  it  for  you.' 

«  Calk  it  ?"  said  Rollo.    «  What  is  that  ? " 
"  Stop  up  the  cracks,  as  they  do  in  ships," 


WATER.  1 1 

said  Jonas.  "When  they  build  ships,  they 
drive  something  into  the  cracks  very  tight 
indeed,  to  prevent  the  water's  leaking  in." 

So  Jonas  went  into  the  shed,  and  present- 
ly returned  with  a  rag.  He  tore  off  a  long 
strip  from  this  rag,  and  laid  it  down  in  the 
water,  just  above  the  board,  and  with  a 
pointed  stick  he  crowded  it  in,  under  the 
board.  Thus  he  stopped  the  leak  almost 
entirely ;  and  he  told  Hollo  that,  by  pumping 
a  little  now  and  then,  he  could  easily  keep 
the  pond  full ;  and  so  he  could  sail  his 
boats  there  as  long  as  he  liked.  He  told 
him  he  might  call  it  the  Red  Sea,  if  he 
pleased ;  for  it  happened  that  the  outside  of 
the  trough  was  painted  red.  "It  will  be  a 
very  pretty  amusement  for  you,  for  one  day" 
said  Jonas ;  "  but  that  will  be  the  end  of  it." 

"  Why,"  said  Rollo,  —  "  what  do  you  mean 
by  that  ? " 

"  0,"  said  Jonas,  "  you  will  get  your  clothes 
all  wet  and  muddy,  and  your  mother  will 
not  let  you  play  there  again." 

"  Ho !  — no  I  sha'n't,"  said  Rollo. 

"  Yes  you  will,"  said  Jonas,  turning  around 
and  walking  backwards.  "  Boys  no  bigger 
than  you  always  like  to  play  in  the  water 
better  than  anything  else ;  but  they  have 


12  WATER. 

not  sense  enough  to  be  careful,  and  so  they 
wet  themselves  all  over.  I  am  coming  back 
in  an  hour,  and  I  shall  find  you  as  wet  as 
a  fisherman." 

Rollo  said  nothing ;  he  was  putting  little 
stones  upon  one  of  his  wooden  blocks,  which 
he  had  taken  for  a  vessel,  and  there  was 
in  his  mind  a  mingled  feeling  of  pleasure 
at  seeing  what  a  cargo  his  ship  would  carry, 
and  of  vexation  that  Jonas  should  think  that 
he  could  not  take  care  of  himself  any  better. 

His  mother  was  sitting,  all  this  time,  at 
the  window  of  her  chamber,  sewing,  and 
she  happened  to  see  and  to  hear  all  that  took 
place.  She,  however,  said  nothing,  but  oc- 
casionally looked  up  to  see  how  Rollo  went 
on.  After  about  half  an  hour,  she  observed 
that  he  seemed  to  give  up  sailing  his  ships, 
and  was  stooping  down,  and  looking  at 
something  very  intently.  He  had  a  small 
stick  in  his  hand,  and  he  appeared  to  be  do- 
ing something  with  that,  which  arrested  his 
attention.  His  mother  watched  him  for  some 
time  fh  silence,  and  at  length  said, 

"  Well,  Rollo,  what  are  you  so  much  inter- 
ested about  ? " 

Rollo  looked  up  surprised ;  and,  when  he  saw 
his  mother  sitting  at  the  window,  he  said, 


WATER.  1 3 

"  O  mother,  only  see  how  this  water 
jumps  up.  I  wish  you  would  come  down 
and  see.  Whenever  I  touch  it  very  gently 
with  this  litue  stick,  it  jumps  up  to  the 
stick." 

"  I  am  busy  now,"  replied  his  mother,  "  and 
cannot  come  down ;  but  you  may  bring  up 
a  little  water  to  me,  in  a  bowl,  and  show 
it  to  me  here." 

So  Rollo  went  in,  and  got  a  bowl,  and 
dipped  up  some  of  the  water,  and  carried 
it  very  carefully  up  stairs  to  his  mother. 
She  told  him  that  he  must  hold  the  bowl 
himself,  for  it  was  wet  outside,  and  she 
would  touch  the  water  with  the  stick. 
She  did  so,  and  found  that,  whenever  she 
touched  it,  the  water  would  jump  up,  as 
Rollo  termed  it,  to  the  stick,  and  rise  in  a 
little  ridge  all  around  it.  But  this  ridge 
was  very  small  indeed. 

"What  makes  it  do  so,  mother?"  said 
Rollo. 

"  I  don't  know,"  said  she. 

"  Don't  you  know,  mother  ? "  said  he,  with 
surprise.  Rollo  was  always  somewhat  sur- 
prised to  find  any  limits  to  his  mother's 
knowledge. 

"  No,"  said  she,  "  I  don't  know  what 
2 


14  WATER. 

makes  it.  I  knew  that  it  would  do  so. 
and  I  knew  several  other  facts  analogous 
to  it.  I  knew  what  name  the  philosophers 
gave  to  them  all ;  but  I  do  not  know  of 
any  cause  for  them." 

"  Analogous  ? "  said  Hollo,  musing,  and 
looking  a  little  at  a  loss. 

"  Yes ;  that  is,  similar  in  their  nature. 
For  instance,"  said  she,  "  look  here,  — 
all  around  the  edge  of  the  water  in  the 
bowl." 

Rollo  looked,  and  saw  that  there  was  a 
little  ridge  of  water  raised  against  the  side 
of  the  bowl,  exactly  like  that  around  the 
stick. 

He  asked  his  mother  what  the  reason 
was  of  such  a  strange  appearance. 

She  answered  that  she  could  not  tell 
what  the  reason  of  it  was.  She  could  only 
tell  what  it  was  called.  She  said  it  was 
called  attraction. 

"  What  is  attraction,  mother  ?  "  said  Rollo. 

"  Attraction  is  drawing  together.  When- 
ever two  things  tend  to  come  together,  each 
drawing  the  other,  it  is  called  attraction. 
The  magnet  attracts  the  little  needle  which 
you  hold  up  towards  it;  that  is,  they  tend 
to  come  together  But  if  you  roll  two  balls 


WATEH.  15 

toward  one  another  upon  the  carpet,  though 
they  come  together,  they  are  not  attracted, 
because  neither  of  them  has  any  influence 
on  the  other ;  they  do  not  make  each  other 
move  at  all.  You  roll  them  together." 

Rollo  listened  to  all  this  very  attentively, 
and  then  looked  upon  the  bowl  again.  He 
did  not  exactly  understand  how  his  mother's 
explanation  applied  to  the  case  of  the  water. 

His  mother  saw  that  Rollo  looked  per- 
plexed. "Don't  you  understand?"  said  she. 

"Not  about  the  water's  jumping  up,"  he 
replied. 

"  Why,  water  attracts  any  thing  that  is 
brought  very  near  it,  —  very  near  indeed. 
So,  when  you  bring  the  stick  down  close 
to  the  water,  it  rises  up  a  little  all  around 
the  stick ;  which  you  call  jumping  up." 

"  Well,  what  makes  it  attract  ? "  said 
Rollo. 

"  I  don't  know,"  said  his  mother ;  "  you 
must  ask  your  father  to-night,  at  tea ;  and 
perhaps  he  can  tell  you.  'He  knows  a 
great  deal  more  about  it  than  I  do." 

Rollo  carried  his  bowl  down  stairs  care- 
fully, and  poured  back  the  water  into  the 
Red  Sea.  When  he  had  done  so,  he  looked 
into  the  bowl,  and  found,  as  he  might  hav« 


16  WATER. 

expected,  that  it  was  wet  still.  Some  of  the 
water  remained  on  the  inside  of  the  bowl; 
running  around  in  drops,  as  he  turned  the 
bowl  in  his  hands.  He  stopped  to  look  at 
it.  It  seemed  to  him  strange,  though  he  had 
never  thought  of  it  before,  that  the  water 
did  not  all  go  out,  and  leave  the  bowl  dry. 

Just  then,  Dorothy  came  out  of  the  kitch- 
en to  the  pump,  with  her  pail  in  her 
hand,  to  pump  some  water.  She  saw  Rollo 
standing  still,  and  looking  into  his  bowl 
with  an  appearance  of  great  attention,  and 
said, 

"  Well,  Rollo,  what  have  you  got  now  ?  " 

Rollo  did  not  answer;  he  was  watching 
the  little  currents  of  water  running  round 
the  inside  of  the  bowl,  as  he  turned  it  over 
and  over. 

"  What  are  you  looking  at,  Rollo  ?  "  she 
inquired  again. 

"  O,  I  am  looking  at  this  bowl.  See," 
said  he,  "I  turn  it  upside  down,  and  yet 
all  the  water  does  not  run  out." 

"  Why,  yes  it  does,"  said  she. 

"No,"  said  Rollo,  "there  is  some  left 
about  the  inside  of  the  bowl.  See,"  he 
continued,  pointing,  "how  wet  it  is." 

"  Poh,  it  is  only  wet ;  all  the  water  has 


WHY  DOESN'T  THE  WATER  DEOP  OFF?-PageIT. 


WATER.  17 

gone  out,  only  the  bowl  is  wet  a  little 
inside,"  she  replied,  pumping  away  into  her 
pail. 

"  But  is  not  wet,  water  ?  "  said  Hollo. 

"  Yes,"  said  Dorothy,  "  I  suppose  it  is." 

"  Then  all  the  water  does  not  fall  out 
of  the  bowl,  when  I  turn  it  upside  down," 
persisted  Rollo. 

"  Why,  you  silly  child,  that's  nothing,  1 
tell  you.  It  always  does  so." 

"But  why  doesn't  it  all  drop  out?"  said 
Rollo,  as  she  took  off  her  pail  from  the  nose 
of  the  pump,  and  walked  towards  the  house. 
"  See,"  he  continued,  following  her,  with 
the  bowl  in  his  hands;  "I  hold  it  bottom 
upwards ;  why  doesn't  the  water  drop  off,  — 
all  of  it  ?  Answer  me  that,  Dorothy ;  answer 
me  that." 

But  Dorothy  paid  no  attention  to  his 
question.  She  went  into  the  house,  and 
shut  the  door.  The  truth  was,  she  would 
have  found  it  somewhat  difficult  to  "  an- 
swer him  that,"  and  she  seemed  to  think  it 
most  prudent  not  to  attempt  it.  Rollo  soon 
got  tired  of  philosophizing  alone,  and  went 
to  sailing  ships  again,  determined  to  ask 
his  father  that  night  at  supper. 

At  length  the  sun  went  down,  the  day 
2* 


18  WATER. 

drew  near  to  its  close,  and  Rollo  found  him- 
self seated  in  the  parlor  ready  for  tea,  — 
the  setting  sun  shining  beautifully  in  at  tho 
windows.  His  lather  came  in,  and  they  aL 
took  their  seats  at  table ;  but  Rollo  had, 
for  some  time,  no  opportunity  to  bring  for- 
ward the  subject  which  interested  him  so 
much,  for  his  father  and  mother  were  very 
busy  talking  about  something  else.  Rollo 
would  not  interrupt  them,  but  kept  looking 
from  time  to  time  towards  his  father.  His 
father  at  length  observed  him,  and  said, 

"Rollo,  have  you  got  any  thing  to  say 
to  me  ? " 

"  Yes,  sir,"  said  Rollo  ;  "  I  want  to  show 
you  an  experiment,  and  have  you  explain 
it  to  me." 

Rollo  then  said  he  wanted  to  go  out  and 
get  a  bowl  of  water,  and  bring  in  to  show 
his  father  what  he  meant ;  but  his  father, 
after  hearing  him  describe  it,  said  he  thought 
he  could  show  the  experiment  just  as  well 
with  his  cup  of  tea.  So  he  brought  down 
the  spoon  very  slowly  and  carefully  to  the 
surface  of  the  tea,  and  Rollo  saw  that  the 
moment  it  touched,  the  tea  immediately 
drew  up  around  the  spoon,  just  as  the 
water  had  risen  around  his  stick.  "Yes, 


\TATEB  19 

father/'  said  he,  "that  is  l^e  experiment^ 
exactly.  Now,  please  to  explain  it  to  me,  fa- 
ther." 

"  Why,  it  is  one  of  the  properties  of  wa- 
ter to  be  attracted  by  almost  any  substance 
which  comes  very  near  it.  But  I  suppose 
you  do  not  know  what  I  mean  by  property." 

"YeSj  sir,  I  do,"  said  Hollo,  eagerly, — 
"it  means  houses,  and  lands,  and  money." 

Here  Rollo  made  a  great  mistake.  In 
fact,  if  he  had  not  been  so  eager  to  show  his 
knowledge,  he  might  have  perceived  in  a 
moment,  that  water  could  not  have  any 
houses,  or  lands,  or  money ;  and  his  father 
was  speaking  of  the  properties  of  water. 

"  That  is  one  meaning,"  said  his  father. 
"  When  we  are  speaking  of  the  property  of 
men,  we  mean  any  thing  that  they  possess. 
But  when  we  speak  of  the  properties  of 
things,  we  mean  something  different.  If  I 
let  the  tongs  drop  upon  the  hearth,  they 
do  not  break;  they  are  strong.  Strength 
is  a  property  of  the  iron.  So  brittleness  is 
a  property  of  glass.  It  is  a  property  of  a 
magnet  to  attract  iron.  A  property  of  any 
substance  is  a  part  of  its  nature,  as  the 
Creator  has  made  it.  Now,  it  is  a  property 
of  water  —  that  is,  it  is  a  part  of  its  nature 


•20 


WAT&R. 


—  to  attract  almost  any  substance  which 
comes  very  near  it." 

"  Mustn't  it  touch  it,  father  ? "  said  Rollo. 

"  What  we  call  touching  it,  is  only  coming 
very  near  it,  —  so  near  that  we  cannot  see  the 
distance  between." 

"  Why,  father,"  said  Rollo,  "  is  there  any 
distance  between  when  it  touches  ? " 

"  Yes,"  said  his  father,  "  very  often  ;  that 
is,  in  Ayhat  we  commonly  call  touching. 
Let  me  see,"  said  he,  thinking;  and  here 
he  turned  and  looked  around  the  room. 
Presently  he  said, 

"  Ah,  I  see  now." 

So  he  rose  from  the  table,  and  took  down 
a  book  from  a  little  mahogany  book-shelf 
behind  him,  and  held  it  with  the  front  edge 
towards  Rollo. 

"  There,  Rollo,"  said  he,  "  do  the  leaves 
of  this  book  touch  one  another  ? " 

"Yes,  sir,"  said  Ro'lo. 

Then  his  father  pressed  the  covers  to- 
gether as  hard  as  he  could ;  and  this 
crowded  the  leaves  into  a  narrower  space, 
although  they  had  appeared  to  touch  before. 

"There;  now  you  see,"  he  continued, 
''  that  they  are  nearer  than  they  were  be- 
fore, though  then  they  seemed  to  touch.  So; 


WATER.  21 

when  you  see  any  two  things  apparently 
touching  one  another,  there  may,  after  all, 
be  a  space  between  them." 

"  I  did  not  know  that  before,"  said  Hollo's 
mother. 

"  Yes,"  said  his  father,  "  I  believe  it  is 
so.  Therefore,  Hollo,  when  I  bring  the  spoon 
down  to  the  water,  at  the  instant  that  the 
water  begins  to  rise  up  around  it,  it  may 
be  that  there  is  a  distance  between,  though 
I  cannot  perceive  it." 

Rollo  was  not  quite  satisfied.  He  thought 
he  could  see  the  spoon  actually  touch,  be- 
fore the  water  moved.  However,  his  father 
told  him  that  it  was  one  of  the  properties 
of  water  to  attract,  and  to  be  attracted  by, 
almost  all  substances,  when  it  came  into  ap- 
parent contact  with  them.  This  kind  of 
attraction  is  called  the  attraction  of  cohesion. 

"  Cohesion  ? "  said  Rollo. 

"Yes,  the  force  with  which  the  particles 
of  the  same  or  of  different  bodies  are  held 
together,  is  called,  in  general,  cohesion. 
Though,  if  we  wish  to  be  precise,  we  call 
it  cohesion  only  when  speaking  of  the  at- 
traction which  the  particles  of  any  one 
substance  have  for  each  other ;  and  when 
we  speak  of  the  attraction  which  they 


5«  WATER. 

have  for  the  particles  of  other  bodies,  we 
call  it  adhesion." 

"  And  which  is  this  ?  " 

"  Why,  strictly  it  is  adhesion ;  for  it  is 
between  the  tea,  or  rather  the  water  of  the 
tea,  and  the  spoon.  But,  then,  the  particles 
of  the  drop  itself  which  hangs  down,  are 
held  together  by  cohesion.  However,  as  the 
nature  of  the  force,  in  the  two  cases,  seems 
to  be  very  nearly  the  same,  it  is  generally 
all  called  the  attraction  of  cohesion." 

"  But  why  does  it  attract,  father  ? "  said 
Rollo. 

"  No  one  knows  of  any  reason,  except  that 
the  Creator  made  it  so." 

"  Does  it  do  any  good,  father  ?  " 

"  Yes,"  said  his  father.  "  It  seems  to 
you  to  be  a  very  little  thing,  and  to  have, 
perhaps,  no  very  useful  tendency ;  and  yet, 
were  it  not  for  this  property  of  water, — 
of  being  attracted  in  this  manner,  and  at 
that  particular  distance,  —  the  most  dreadful 
consequences  would  result  to  all  mankind." 

"  Why,  father ! "  said  Rollo,  in  a  tone  of 
surprise  ;  "  what  consequences  ? " 

"  I  will  tell  you.  But  first  I  will  tell  you 
some  of  the  smaller  inconveniences  we  should 
have  to  bear,  and  then  the  more  important 


WATER.  23 

ones.  One  difficulty  would  be,  that  I  could 
not  write  any  more  with  ink." 

"  Why  not ' "  said  Rollo. 

His  father  then  dipped  his  spoon  a  little 
way  into  the  tea,  as  he  would  have  dipped  a 
pen  into  the  inkstand,  and,  taking  it  up,  a  little 
drop  of  tea  hung  at  the  tip  of  it,  just  like 
the  ink  in  the  pen.  "  There,"  said  he,  "  you 
see  that  is  the  way  I  take  up  my  ink.  Now, 
if  the  ink  was  not  attracted  to  the  pen  so,  it 
would  not  come  up ;  my  pen  would  come  out 
of  the  inkstand  as  dry  as  it  went  in." 

"  Would  it  ?  "  said  Rolio,  with  surprise. 
"  But  that  is  ink,  and  you  were  talking  about 
water." 

"  Yes,"  said  his  father,  "  but  it  is  just  the 
same  with  ink.  In  fact,  ink  is  only  water 
colored  very  black." 

"  Could  not  you  get  any  in  your  pen  ?  "  said 
Rollo,  —  "  not  any  at  all  ?  " 

"  No,"  said  his  father ;  "  unless  it  were  at- 
tracted to  the  pen,  it  would  not  adhere  to  it 
at  all.  The  pen  would  come  out  dry  and 
clean,  as  it  went  in." 

"Why,"  said  Rollo,  "how  funny  that 
would  be  !  I  should  like  to  see  such  ink  as 
that." 

"That  is  the  way  it  would  operate,"  said 


&4  WATER. 

his  father,  "  undoubtedly ;  and  if  you  were 
to  dip  your  fingers  in  it,  it  would  be  just  so ; 
they  would  come  out  clean  and  dry.  In  fact, 
if  I  should  throw  it  over  your  face  and  clothes, 
it  would  all  fall  off  upon  the  ground,  and  leave 
you  just  as  you  were  before." 

"  Why,  father  !"  said  Rollo  ;  and  he  laughed 
outright  at  the  idea  of  his  father's  throwing 
ink  all  over  him,  and  especially  of  its  falling 
off  in  that  manner.  In  fact,  it  was  hard  for 
him  to  believe  that  it  was  possible  for  such  a 
thing  to  be. 

"  I  cannot  show  you  any  ink  that  will  act 
so ;  but  I  can  show  you  another  liquid  that 
will.  There  are  some  liquids  that  do  not  thus 
attract  other  substances  ;  and  if  you  dip  things 
into  them,  they  come  out  clean  and  aty. 

"  Are  there,  father  ? "  said  Rollo ;  "  I  never 
saw  any." 

"  I  will  show  you  one,"  said  his  fathei, 
"after  the  tea  things  are  moved  away  from 
ihe  table." 


QUESTIONS. 

How  did  Rollo  first  attempt  to  dam  up  the  open  side  of 
the  trough?  How  did  Jonas  attempt  it?  How  long  did 
Jonas  suppose  the  pleasure  of  sailing  boats  in  the  ponJ 


WATER.  25 

would  last  ?  Why  not  longer  ?  Was  Jonas  right  or  wrong 
in  his  expectations  ?  What  phenomenon  attracted  Hollo's 
attention  ?  Did  you  ever  notice  this  appearance  ?  Did 
you  ever  think  of  inquiring  into  the  reason  of  or  nature  of 
it  ?  Did  it  ever  appear  to  you  to  be  anything  remarkable ? 
Do  you  think  now  it  is  anything  remarkable  ?  Whom  did 
Hollo  first  ask  about  it  ?  Did  she  know  any  tiling  about 
it?  Did  she  know  that  she  was  ignorant?  Whom  did  he 
apply  to  next  ?  What  did  his  mother  say  about  it?  Where 
was  Hollo's  father  when  he  first  asked  him  about  the  case  ? 
How  did  his  father  perform  the  experiment?  What  did 
he  say  was  the  name  to  the  property  of  water  which  Hollo 
had  observed  ?  What  is  the  difference  between  cohesion 
and  adhesion  ?  Was  it  cohesion  or  adhesion,  strictly 
speaking,  which  Hollo  had  observed  ?  Which  is  it  which 
causes  the  drop  to  assume  its  round  form  ?  Which  is  it 
which  causes  the  drop  to  remain  suspended  from  the 
spoon?  Are  not  both  generally  called  cohesion  ? 


CHAPTER    II. 

WATER. 

VERY  soon  after  this,  they  rose  from  the 
table,  and  Dorothy  came  in,  and  began  to  take 
away  the  waiter  and  the  cloth.  Hollo  put 
his  chair  back,  and  then  went  to  a  table  at 
the  back  side  of  the  room,  and  dipped  the 
pen  into  an  inkstand  that  was  there.  He 
saw  the  ink  adhering  to  the  pen,  and  was 
satisfied  that,  unless  it  had  been  consider- 
ably attracted  by  the  pen,  it  would  all  have 
fallen  off,  at  once,  back  into  the  inkstand. 

JVhile  he  was  looking  at  this,  his  father, 
who  had  before  gone  out  of  the  room,  came 
back  with  a  small  and  very  short  glass 
phial  in  his  hands,  which  he  put  down 
upon  a  corner  of  the  table.  Rollo  went 
up  to  look  at  it.  His  father  did  not  tell 
him  not  to  touch  it,  as  he  knew  he  would 
not  touch  it  without  leave.  His  moth 
or  asked  them  to  wait  until  she  was 
ready  to  come  in  from  the  kitchen ;  and 
while  she  was  gone,  Rollo  stood  looking 


WATER.  2"i 

at  the  phial.  It  seemed  to  be  full  of  some- 
thing which  was  of  a  kind  of  grayish  color. 
He  asked  his  father  if  he  might  take  it 
up.  His  father  said  that  he  might  lift  it 
up  once  gently,  and  then  put  it  down 
again.  He  took  it  up  carefully,  by  the  neck 
of  the  phial,  and  then  immediately  put  it 
down,  saying,  "  O,  how  heavy ! " 

In  a  short  time,  Hollo's  father  came  to 
the  table,  bringing  in  his  hand  a  saucer, 
a  sheet  of  white  paper,  and  a  knitting 
needle  ;  and,  sitting  down,  he  said  that  he 
was  going  to  wait  until  Hollo's  mother 
was  ready.  He  also  asked  her  to  bring  a 
tea-spoon  with  her,  when  she  should  come. 

In  a  few  minutes,  she  came  with  a 
tea-spoon;  then  Hollo's  father  took  up  the 
little  phial,  and  said, 

"  This  is  mercury  in  this  phial ;  or,  as 
they  call  it  sometimes,  quicksilver."  So  he 
uncorked  it,  and  poured  it  out  into  the 
saucer.  It  came  out  in  a  fine  stream,  like 
melted  lead,  and  fell  into  the  saucer  as  if 
it  was  very  heavy. 

"  The  reason  that  I  have  brought  this 
out  to  you,  Hollo,"  said  his  father,  "  is,  that 
it  differs  from  water  in  not  having  any 
apparent  cohesion  for  most  other  substances ; 


28  WATER. 

—  so  we  can  see,  a  little,  by  means  of  it, 
how  water  would  appear,  if  water  had  none 
Now,  Rollo,  go  and  get  a  pen,  and  dip  it 
in,  and  see  if  you  can  take  up  a  pen  full, 
as  if  it  were  ink." 

So  Rollo  went  to  the  table,  and  brought 
a  clean  pen,  and  dipped  the  point  into  the 
mercury ;  but,  instead  of  the  mercury's  "jump- 
ing up,"  as  the  water  had  done,  the  pen  seemed 
to  make  a  deep  pit  or  depression  all  around 
itself  in  the  mercury ;  and  when  he  took  the 
pen  out,  it  was  as  dry  as  when  it  went  in. 

"Why,  father,"  said  Rollo;  "it  don't 
seem  to  like  the  pen." 

"No,"  said  his  father,  "it  nkes  itself  bet- 
ter than  it  likes  the  pen.  That  is  the 
difference  between  mercury  and  water. 
Water  has  the  property  of  cohering,  or  ad- 
hering, pretty  strongly  to  other  substances ; 
but  mercury  has  the  strongest  attraction 
for  itself.  So,  when  you  dip  a  pen  into 
water,,  the  water  that  is  close  around  the 
pen,  coheres  more  strongly  to  the  pen  than 
it  does  to  the  other  water ;  and  when  you 
take  the  pen  out,  this  small  portion  of 
water  comes  up  with  it.  But  when  you 
put  the  pen  into  the  mercury,  the  mercury 
that  is  close  about  the  pen  ir  ""^re  attract^ 


WATER.  29 

by  the  other  mercury  than  it  is  by  the 
pen.  So  it  recedes  from  the  pen ;  it  shrinks 
away  from  it,  as  it  were  ;  and  when  you 
take  the  pen  out,  none  of  the  mercury 
comes." 

"  Is  that  the  way  of  it  ? "  said  Rollo. 

"  Yes,"  said  his  father ;  "  and  this  sim- 
ple difference  in  the  cohesive  properties  of 
water  and  mercury,  gives  rise  to  great  dif- 
ferences in  the  phenomena  that  the  two 
liquids  exhibit." 

While  Rollo's  father  was  saying  this,  he 
observed  that  Rollo  was  dipping  the  pen 
in  and  out  of  the  mercury,  and  was  not 
paying  much  attention  to  what  he  was 
saying.  In  fact,  what  he  was  saying  was 
rather  too  difficult  for  Rollo  to  understand, 
without  attending  pretty  closely. 

"Put  the  pen  down  a  minute,  Rollo," 
said  his  father,  "  and  listen  to  me ;  and 
presently  you  may  try  experiments." 

So  Rollo  put  the  pen  down  at  once,  and 
looked  up  at  his  father. 

"I  want  to  tell  you  what  great  differ- 
ences there  are  between  water  and  mer- 
cury, arising  out  of  this  fact,  that  water 
coberes  to  other  things,  and  mercury  does 
not.  It  follows  from  it  that,  if  you  dip 
2* 


30  WATER. 

anything  into  water,  the  water  rises  around 
it,  and  spreads  over  its  surface ;  and  some 
water  comes  up  with  it,  when  you  take  it 
out.  But  if  you  dip  anything  in  mercury, 
the  mercury  is  depressed  around  it,  instead 
of  being  raised,  and  it  does  not  come  up  with 
it  at  all,  when  you  take  it  out.  For  the 
same  reason,  if  you  pour  out  a  little  wa- 
ter upon  a  table,  it  spreads  around  upor 
it,  and  you  cannot  take  it  up  again.  If 
you  pour  out  a  little  mercury,  on  the  other 
hand,  it  does  not  adhere  to  the  table,  but 
rolls  about  in  little  balls,  and  you  can  take 
it  up  clean  with  a  spoon." 

"  O,  let  me  try,  father,"  said  Rollo. 

"  Presently,"  replied  his  father.  "  Another 
different  result  is,  that  if  you  pour  water 
upon  anything  that  has  small  pores  or  in- 
terstices, like  sponge,  or  cloth,  or  earth,  it 
penetrates  to  every  part,  and  coheres  to  every 
part,  and  keeps  it  all  wet.  But  mercury 
would  'remain  in  a  mass  at  the  top,  if  the 
pores  were  very  small ;  and  if  they  were 
large  enough  to  allow  it  to  penetrate  at 
all,  it  would  all  run  off  below,  leaving  the 
whole  dry." 

"How?"  said  Rollo. 

"  Why,  if  you  were  to  make  a  little  heap 


WATER.  3 I 

of  earth  and  gravel-stones,  with  a  hollow 
place  upon  the  top,  and  then  pour  water 
upon  it,  it  would  gradually  soak  in,  as  we 
call  it;  that  is,  it  would  diffuse  itself  all 
through  the  heap,  and  make  it  all  wet. 
i>ut  if  you  were  to  pour  mercury  into  the 
hollow,  it  would  either  remain  there  with- 
out going  down  at  all,  or  else,  if  the  spaces 
in  the  gravel  were  great  enough  to  let  it 
pass  down,  it  would  all  run  down  together, 
entirely  through,  and  would  not  cohere  to 
the  gravel  at  all." 

"  Where  would  it  go  to  ? "  said  Hollo. 

"  Down  as  low  as  it  could  get ;  and  there 
you  would  find  it,  all  together,  or  as  much 
together  as  it  could  be." 

Hollo's  father  then  took  up  a  little  of 
the  mercury  with  the  tea-spoon,  though  it 
was  difficult  to  do  it ;  for  it  cohered  to  it- 
self so  strongly,  and  had  so  little  attrac- 
tion for  the  silver,  that  it  seemed  to  be 
actually  repelled.  This,  however,  was  owing 
to  the  fact,  that  the  silver  was  not  per- 
fectly bright  «and  clean.  Hollo  had  been 
handling  it,  and,  though  it  looked  clean,  it 
was  really  covered  with  a  very  thin  and 
invisible  film  of  moisture  from  his  fingers, 
which  kept  the  mercury  from  coming  into 


32  WATER. 

actual  contact  with  the  metal.  At  length, 
however,  his  father  succeeded  in  taking  up 
a  small  portion,  and  he  then  poured  it  out 
gently  upon  the  sheet  of  paper;  it  rolled 
out  like  a  sort  of  liquid  ball.  Hollo  amused 
himself  for  some  time  in  pushing  it  about, 
and  dividing  it  into  parts  with  the  knitting 
needle.  He  observed  that  when  he  divided 
it  into  small  parts,  these  parts  were  always 
round,  like  little  balls ;  his  father  called 
them  globules.  When  he  brought  two  of 
these  globules  together,  they  would  instant- 
ly unite  into  one  ball,  perfectly  round  and 
bright ;  unless  it  was  a  pretty  large  one, 
and  then  it  was  flattened  a  little  at  the 
top.  His  father  explained  to  him  that  the 
reason  why  the  mercury  always  took  that 
form,  was  because  the  particles  attracted 
each  other  strongly,  and  consequently  they 
were  all  drawn  in  from  every  side  towards 
the  centre ;  and  from  this  resulted  the  glob- 
ular form. 

"  Father,"  said  Rollo,  at  length,  "  I  think 
the  reason  why  the  mercury  does  not  stick 
to  the  pen  and  to  my  fingers,  like  ink,  is 
because  it  is  so  heavy.  When  you  take 
the  pen  out,  the  mercury  is  so  heavy  that 
it  falls  directly  back  again. 


WATER.  33 

"  No,"  said  his  father,  "  that  cannot  be 
the  reason,  because  that  would  not  prevent 
its  spreading  out  over  the  paper,,  or  upon 
the  table,  and  cohering  to  that.  It  is  true 
it  is  a  great  deal  heavier  than  water,  but 
that  does  not  occasion  these  different  effects. 
It  is  the  nature  of  the  substance,  in  not  co- 
hering to  other  substances.  Now,  there  are 
some  things  that  water  does  not  cohere  to." 

"Are  there?"  said  Hollo ;  "what?" 

"Oily  substances,  the  feathers  and  fur 
of  some  animals,  and  some  plants.  Water 
rolls  off  from  a  cabbage  leaf,  just  as  mer- 
cury does  from  paper.  So  it  does  from 
feathers.  A  goose  does  not  get  wet  by 
floating  on  the  pond;  and  a  duck's  head 
comes  up  from  the  mud  as  bright  and  dry 
as  it  went  down." 

"  Yes,  I  have  seen  it,  father,"  said  Hollo. 

"And  so  with  the  furs  of  animals  that 
live  in  the  water." 

"Yes,"  said  Rollo,  "Jonas  says  that  he 
has  seen  a  water  rat  come  up  out  of  wa- 
ter as  dry  as  mother's  muff." 
.  "  And  then,  again,"  continued  his  father, 
"  there  are  some  substances  that  mercury 
will  adhere  to.  For  instance,  if,  instead  of 
this  sheet  of  paper,  I  had  taken  a  sheet  of 


34  WATER. 

perfectly  clean  and  bright  tin,  and  put  a 
globule  of  mercury  upon  it,  it  would  have 
spread  itself  out  upo;i  it,  and  wet  it,  as  it  were, 
like  water  upon  wood. 

"  But  now,  Rollo,"  continued  his  father,  "  I 
must  go.  You  may  play  with  this  mercury  a 
little  while,  and  then  your  mother  will  put  it 
away  for  me." 

"  Yes,  but,  father,"  said  Rollo,  "  you  were 
going  to  tell  me  of  some  terrible  consequences 
which  would  come  from  there  being  no  cohe- 
sion." 

"Yes, — no  cohesion  between  water  and 
other  substances,"  said  his  father,  rising,  and 
standing  by  his  chair,  ready  to  go.  "  Well,  I 
will  tell  you. 

"First,"  said  he,  "we  could  never  write 
with  pen  and  ink ;  for,  if  the  water  had  no 
attraction  for  the  pen,  it  would  not  come  up 
from  the  inkstand ;  and  then,  if  it  had  no 
attraction  for  the  paper,  it  would  not  leave  the 
pen  and  go  to  the  paper  when  we  move  the 
pen  along." 

"  Yes,  sir,"  said  Rollo,  "  you  told  me  that 
before." 

"  Then,  secondly,"  continued  his  father, 
<  we  could  never  wash  any  thing.  Suppose, 
ii'ter  you  have  been  painting,  some  day,  you 


WATER.  35 

want  to  wash  off  the  paint  that  is  left  upon 
the  saucer.  You  dip  it  into  water.  The 
water  adheres  to  the  paint  and  to  the  saucer, 
and,  when  you  rub  it  a  little,  the  water  and 
the  paint  move  together,  and  fresh  water 
poured  on  carries  it  all  off.  So,  if  the  paint 
were  upon  a  cloth,  the  water  would  penetrate 
among  all  the  fibres  of  the  cloth,  and  unite 
with  the  particles  of  paint  there,  and  bring 
them  out.  But  you  could  not  wash  anything 
out  with  mercury. 

"  Nor  can  you  wash  anything  out  with 
water,  unless  it  is  of  such  a  nature  that  watei 
has  cohesion  for  it.  For  instance,  you  cannot 
wash  out  a  spot  of  oil,  because  water  and  oil 
do  not  cohere.  The  water  does  not  take  hold 
of  it,  as  it  were.  And  so,  if  water  had  no  co- 
hesion for  any  thing  but  itself,  nothing  could 
be  washed.  Your  hands  would  come  out  of 
it  just  as  they  went  in.  If  it  was  poured 
upon  clothes,  it  would  all  run  off  directly. 
You  could  not  take  it  up  with  a  sponge,  nor 
wet  anything  with  it  whatever. 

"  But,  in  the  third  place,  the  worst  conse- 
quence of  all  would  be  this.  The  water  is 
retained  in  the  ground  by  the  attraction  be- 
tween it  and  the  particles  of  earth.  If  it 
were  not  for  this,  it  would  not  remain  up  near 


OO  WATER. 

the  surface,  but  would  all  run  down  through 
the  strata  of  earth  to  the  lowest  place  it  could 
get  to,  and  leave  the  upper  part  of  the  ground 
entirely  dry.  After  a  heavy  shower  of  rain, 
the  3arth  would  be  as  dry  as  befc  re  ;  a  great 
part  of  the  water  would  run  off  in  little  drib- 
bling streams,  like  a  stream  of  mercury  ;  and 
the  rest  would  go  down  through  the  ground 
at  once,  as  a  shower  of  shot  would,  through  a 
heap  of  large  stones.  Of  course  all  plants 
would  die,  the  earth  would  be  parched  up,  and 
men  and  animals  famish.  Were  it  not  for  this 
property  of  water  to  cohere  to  itself,  and  to 
adhere  to  other  things,  every  plant  and  tree 
would  wither  and  die  for  want  of  water  in 
twenty-four  hours,  even  if  it  was  raining  all 
the  time." 

"  What !  if  it  rained  all  the  time  ?  "  said 
Rollo. 

"Yes,  every  moment,"  said  his  father. 
"  The  rain  would  come  down  upon  the  plants 
and  their  roots,  as  this  mercury  would  upon  a 
quill  top.  It  would  roll  off  in  globules,  and 
not  wet  them  at  all." 

Here  Hollo's  father  began  to  move  away, 
saying  to  Rollo  that  he  had  better  observe 
carefully  all  the  cases  of  cohesion  that  he 
might  meet  with,  and  that  he  would  tell  him 


WATER.  39 

more  about  it  some  other  time.  He  had, 
however,  not  gone  far  from  the  table  before 
Rollo  called  him  back,  saying,  in  a  voice  of 
great  interest  and  surprise, 

"  O  father,  father,  see  how  bright  your 
spoon  is ! " 

His  father  turned  round  suddenly,  and  said, 
«  Where  ? " 

Rollo  handed  him  the  spoon.  In  the  mid- 
dle of  the  bowl,  there  was  a  large  bright 
patch,  —  very  bright  indeed.  He  took  it, 
looked  at  it  a  moment,  and  said,  in  a  low  tone, 
as  if  he  was  talking  to  himself, 

"  Why  !  —  how  foolish  I  was  !     How  fool 
ish  I  was  !  " 

"  What ! "  said  Rollo.  «  What !  What  is 
it?" 

"  I  might  have  known  better  than  that," 
said  his  father,  still  musing. 

"  What  is  it,  father  ? "  said  Rollo,  eagerly. 

"  Why,  I  might  have  known  that  the  mer- 
cury would  have  united  with  the  silver  ;  but 
I  did  not  think  of  it.  You  see,  Rollo,  that  here 
is  a  spot  that  the  mercury  has  '  wet,'  as  you 
call  it.  Silver  is  one  of  those  substances  that 
the  mercury  has  an  attraction  for ;  and  it  has 
united  with  it,  and  I  don't  know  how  we 
shall  get  it  oif. 


40  ,         WATER. 

"However,"  he  continued,  "it  will  do  to 
illustrate  what  I  have  been  saying.  If  you 
put  a  little  mercury  upon  this  spot,  you  will 
find  that  it  will  cohere  now,  and  will  spread 
all  over  it,  like  water  upon  a  board." 

Rollo  tried  the  experiment.  He  rolled  a  lit- 
tle globule  of  mercury  into  the  spoon,  and,  the 
moment  it  touched  the  bright  spot,  it  spread 
all  over  it  at  once;  and,  when  he  turned 
the  spoon  over  again,  it  did  not  fall  off.  His 
father  then  rubbed  it  off  as  well  as  he  could, 
but  it  only  made  the  spot  larger  and  brighter. 

"Father,"  said  Rollo,  "I  think  you  had 
better  rub  the  mercury  over  all  your  spoons." 

His  father  smiled,  and  said  he  would  proba- 
bly think  differently  when  he  should  come 
to  see  it  the  next  morning.  But  he  gave 
Rollo  a  small  piece  of  money  which  he  told 
him  he  could  brighten  all  over  in  the  same 
way  if  he  wished. 

"  Why  not  the  spoon  ? "  said  Rollo. 

"  Why,  to-morrow  morning,"  said  his  fa- 
ther, "  all  this  brilliancy  will  be  gone,  and  the 
silver  will  look  tarnished  and  dull." 

"  Then  how  can  you  get  it  bright  again  ? " 
asked  Rollo. 

'•  I  do  not  know,"  said  his  father ;  "  I  must 
ask  some  chemist." 


WATER.  41 

It  turned  out  that  this  was  not  necessary ; 
for,  in  the  morning,  Hollo's  mother  rubbed  the 
dull  spot  off,  with  a  little  whiting.  But  mer- 
cury ought  to  be  used  very  carefully ;  for,  if  the 
little  globules  get  upon  any  thing  that  is  of 
silver,  as,  for  example,  a  spoon,  a  watch,  a 
thimble,  or  a  pencil-case,  they  immediately 
combine  with  the  silver,  producing  spots 
which  it  is  sometimes  troublesome  to  remove. 
The  kind  of  attraction,  however,  between  the 
silver  and  the  mercury,  is  thought  by  the 
philosophers  to  be  of  a  different  kind  from 
that  between  water  and  glass,  for  example, 
although,  in  most  respects,  it  is  of  a  nature 
very  similar 


QUESTIONS. 

What  substance  did  Rollo'a  father  bring  to  show  to 
Rollo  and  his  mother  after  tea  ?  In  what  sort  of  a  vessel 
was  it  contained  ?  Why  do  you  suppose  it  was  necessary 
to  have  the  phial  short  ?  What  was  the  first  experiment 
which  Hollo's  father  performed  with  the  mercury  ?  What 
is  the  name  by  which  mercury  is  commonly  known  ? 
What  was  the  effect  produced  when  a  pen  was  dipped  into 
it  ?  What  did  Rollo  suppose  was  the  reason  why  the  mer- 
cury did  not  adhere  to  the  pen  or  the  fingers?  How  did 
his  father  prove  to  him  that  this  was  not  the  reason  ? 
What  effect  did  the  mercury  produce  upon  the  spoon." 
Would  it  have  produced  any  such  effect  if  the  spoon  had 
been  of  glass.' 

6*  4* 


CHAPTER    III. 
THE  THREE   DIFFICULTIES. 

THE  next  morning,  Hollo  was  going  across 

e  yard  towards  the  pump,  carrying  a  paper 
boat,  which  he  was  going  to  sail  in  his  sea, 
when  Jonas  met  him. 

"  Ah,  Jonas,"  said  he,  "  you  did  some  good 
by  making  that  sea  for  me  yesterday.  I've 
learned  all  about  water  by  means  of  it." 

"  What,  all  about  water  ?  "  said  Jonas. 

"  Why,  —  not  quite  all,  perhaps  ;  but  all 
about  cohesion,  at  any  rate." 

"  Yes,  I  read  about  cohesion  once  in  a  book, 
and,  if  you  have  learned  all  about  it,  you  have 
learned  a  great  deal.  However,  boys  gen- 
erally learn  all  about  a  thing  a  great  deal 
quicker,  when  they  are  as  big  as  you,  than 
when  they  grow  older." 

Hollo  saw  that  Jonas  said  this  with  a  sort  of 
sly  look  ;  and  in  fact  he  had  so  often  laughed 
at  him  for  vanity  and  self-conceit,  whenev- 
er he  exhibited  these  foibles,  that  he  knew 
now  that  he  was  really  ridiculing  his  preten 


THE    THREE    DIFFICULTIES.  43 

to  have  understood  completely  a  difficult 
philosophical  subject  so  easily.  He  looked  a 
little  ashamed;  but  Jonas  presently  relieved 
him  by  saying  that  he  was  going  to  drive  the 
cow  to  pasture,  and  asking  Hollo  to  go  with 
him,  and  tell  him  what  he  had  learned  by 
the  way. 

Rollo  asked  his  mother's  leave,  and  then 
they  went  along,  Rollo  having  first  put  his 
paper  boat  down  by  the  side  of  the  pump. 
As  they  walked  along,  Jonas  asked  Rollo  to 
tell  him  what  he  had  learned  about  the  at- 
traction of  cohesion  ;  and  so  Rollo  repeated, 
as  well  as  he  could,  his  father's  conversation. 
He  told  him  that  the  particles  of  water  co- 
hered to  each  other,  and  adhered  to  almost 
all  other  substances,  whenever  they  came  in 
contact  with  them.  On  the  whole,  he  gave 
the  substance  of  the  information  which  he  had 
received,  pretty  correctly ;  though,-  as  usual 
with  beginners  in  all  studies,  he  spoke  fai  too 
confidently,  and  made  his  assertions  in  too 
general  and  unlimited  a  manner. 

11  Very  well,"  said  Jonas ;  "  I  read  some- 
thing about  it  in  a  book  once,  and  I  should 
like  to  have  you  answer  me  some  questions  I 
thought  of." 

"  Well,  I  will,"  said  Rollo. 


44  WATEU. 

"  If  you  cai ,"  said  Jonas. 

"  O.  I  think  I  can,"  said  Rollo,  "  for  father 
explained  it  all  to  me,  perfectly." 

"  The  first  question  is  the  dropping  ques- 
tion," said  Jonas.  "  When  I  try  to  drop  any 
medicine  from  a  phial,  after  it  gets  a  going,  it 
Jrops  well  enough ;  but  at  first  it  won't  run 
easily.  It  acts  just  as  you  say  the  mercury 
does.  It  keeps  back  in  the  phial,  and  heaps 
up  at  the  edge,  and  does  not  want  to  go  along 
over  the  glass." 

"  O,  that  is  because  the  glass  is  dry,"  said 
Rollo,  readily.  "  You  must  wet  it  with  your 
finger,  and  then  it  will  run.  That  is  the  way 
my  mother  does." 

"  Yes,  but  why  don't  it  run  of  itself,"  re- 
joined Jonas,  "  and  wet  its  own  way  ?  If 
there  is  an  attraction  between  the  glass  and 
the  water,  why  don't  the  water  move  right 
along  over  it  ? " 

"  I  don't  know,"  said  Rollo,  shaking 
his  head  seriously.  "  I  mean  to  ask  my  fa- 
ther." 

"  The  next  question  is  the  drying  question. 
If  you  wet  a  piece  of  board,  and  then  leave  it 
a  little  while,  when  you  come  back,  the  water 
is  all  gone." 

"  Yes,  it  has  dried  up,"  said  Rollo. 


THE    THREE    DIFFICULTIES.  45 

"Yes,  but  it  must  have  gone  away  some- 
where," said  Jonas. 

"  No,"  said  Hollo,  "  it  has  dried  up ;  it  has 
not  gone  away." 

"  Why,  yes,"  replied  Jonas,  "  it  must  have 
gone  away  somewhere.  You  see,  when  I 
leave  the  board,  the  water  is  there  ;  and  when 
I  come  again,  it  is  not  there  :  of  course  i1; 
must  be  gone." 

"  It  is  aJ  gone  to  nothing,"  said  Rollo. 

"  Ho  ! "  said  Jonas,  "  I  know  better  than 
that  myself.  I  don't  think  you  answer  the 
second  question  any  better  than  the  first." 

"  Why,  I  don't  see  any  question  about  it," 
said  Rollo.  "  It  hasn't  anything  to  do  with 
cohesion." 

"  Why,  if  there  is  an  attraction  between 
the  water  and  the  board,  why  doesn't  it  keep 
them  together  ? " 

Rollo  insisted  that  the  water  all  dried  up 
"  to  nothing,"  as  he  termed  it ;  and  yet  he 
was  not  very  well  satisfied  with  his  explana- 
tion himself;  but  he  was  very  unwilling  to 
admit  that  he  could  not  answer  any  of  Jo- 
nas's  questions. 

"  Well,  what  is  the  third  question,  Jonas  ?  " 
said  he. 

"  The  third  is  about  the  water  balls.    I  can 


46  WATER. 

make  water  globules  just  like  the  mercury 
globules." 

"  Can  you  ?  "  said  Rollo  ;  "  on  what  ?  " 

"  On  water  itself." 

"  O  Jonas ! "  said  Rollo,  with  a  tone  ol 
great  incredulity. 

"  I  can,"  said  Jonas.  "  I  have  seen  them 
a  hundred  times,  when  I  was  playing  in  the 
water.  If  you  spatter  the  water  when  the  sun 
shines  on  it  so  that  you  can  see  clearly,  you 
will  see  little  balls  about  as  big  as  shot,  rolling 
about  in  all  directions,  growing  smaller  and 
smaller,  until  they  become  only  a  little  point, 
and  then  they  vanish." 

"  They  are  bubbles,"  said  Rollo. 

"  No,"  said  Jonas ;  "  there  are  little  bubbles 
too,  but  they  look  very  different  from  the 
water  balls." 

Rollo  said  that  he  wished  Jonas  would 
show  him  some,  and  Jonas  promised  to  try 
and  see  if  he  could  make  them  as  soon  as  he 
should  get  back  to  the  pump. 

He  did  so,  and  he  succeeded  very  well. 
Rollo  saw  the  little  globules  very  distinctly. 
They  were  different  in  their  form  from  the 
bubbles ;  and  then,  besides,  they  rolled  away 
very  swiftly  over  the  water,  while  the  bubbles 
floated  very  slowly,  or  remained  nearly  at  rest. 


THE   THREE   DIFFICULTIES.  4i 

"Now,"  said  Jonas,  "if  the  particles  of 
water  attract  one  another,  why  don't  these  lit- 
tle globules  spread  right  out,  at  once,  all  over 
the  surface  ? " 

"  Or  sink  in  ? "  said  Hollo. 

"  Yes,"  said  Jonas. 

"  I  don't  know,"  said  Rollo ;  and  he  ter- 
minated the  discussion  in  the  usual  way,  by 
saying,  "  I  mean  to  ask  my  father."  Jonas 
then  went  off  to  his  work,  and  Rollo  continued 
for  some  time  at  the  pump,  amusing  himself 
with  making  the^e  water  globules.  At  length, 
ne  got  tired,  and  his  paper  boat,  after  floating 
a  short  time,  got  gradually  soaked  through, 
and  lay  down  upon  her  side,  half  submerged, 
like  a  vessel  water-logged,  as  the  sailors  say. 
Rollo  then  went  in  the  house  to  find  his  fa- 
ther. 

His  father  had  gone  away;  but  he  found 
his  mother  at  work  in  the  parlor.  She  called 
him  to  come  and  read  to  her ;  for,  as  Rollo  did 
i:ot  go  to  school  now,  he  used  to  read  to  his 
mother,  and  have  some  lessons  besides,  every 
day.  After  finishing  the  reading  lesson,  he 
concluded  to  propose  Jonas's  questions  to  his 
mother. 

She  heard  them  with  a  good  deal  of  interest, 
and  said  she  could  not  answer  but  one  of  tnem. 


48  WATER. 

"  Which  is  that  ? "  said  Rollo. 

"The  second,  —  the  drying  question,  as 
you  call  it.  Get  your  chair,  and  come  and 
sit  down  here,  and  I  will  give  you  a  1  ttle 
lecture  upon  evaporation." 

So  Rollo  got  his  chair,  and  took  his  seat 
opposite  to  his  mother,  and  she  began  her 
lecture  in  the  following  words  :  — 

"  Your  father  explained  to  you  that,  when 
water  is  spilled  upon  wood,  there  is  an  attrac- 
tion between  the  wood  and  the  water,  so  that 
it  adheres  to  the  wood;  and,  in  fact,  that 
there  is  a  similar  attraction  between  water  and 
almost  all  solid  substances." 

"  Yes,  mother,"  said  Rollo. 

"  Now,  there  is  another  substance  which 
also  has  a  very  peculiar  attraction  for  water, 
and  this  attraction  produces  very  singular  ef- 
fects, —  very  singular  effects  indeed." 

"  What  substance  is  it  ?  "  said  Rollo. 

"  The  air,"  replied  his  mother. 

"The  air?" 

"  Yes,  the  air ;  which  is  all  about  us  in  the 
room,  and  out  of  doors.  It  is  very  thin  ;  but 
you  can  feel  it  when  you  move  your  hand 
back  and  forth,  —  so." 

Here  Rollo's  mother  moved  her  hand  back 
and  forth  rapidly,  and  Rollo  did  the  same. 


THE    THREE    DIFFICULTIES.  49 

He  could  distinctly  feel  the  impulse  of  the  air 
upon  his  hand. 

"Now,  this  air  has  a  strong  attraction  for 
water,  and  when  any  water  is  lying  upon  a 
board,  and  the  air  is  over  it,  the  air  gradually 
takes  it  up." 

"  Takes  it  up  ?  —  why,  how,  mother  ?  " 

"  It  attracts  it,  and  the  particles  of  water 
rise  up,  one  after  the  other,  and  mingle  with 
the  air,  and  float  away. 

"  We  cannot  see  them,  for  they  are  very 
small,  and  they  rise  very  gradually ;  and  they 
make  no  difference  in  the  appearance  of  the 
air,  when  they  have  mingled  with  it.  It  is 
something  like  sugar  dissolving  in  a  cup  of 
warm  water.  The  water  has  an  attraction  for 
the  sugar,  and  takes  the  particles  off  from  it 
gradually,  and  floats  them  away,  until  all  the 
sugar  is  diffused  equally  over  the  whole  cup 
of  water.  So  the  air  takes  up  the  water.  This 
is  what  we  call  drying.  It  is  the  water  going 
off  into  the  air,  because  the  air  has  a  stronger 
attraction  for  it  than  the  solid  substance  it 
rests  upon.  But  oil  will  not  dry  up  in  that 
way.  If  you  pour  oil  upon  a  board,  and  leave 
it  for  months,  when  you  come  back,  yoa  will 
find  it  oily  still.  This  is  because  there  is  a 
stronger  attraction  between  the  oil  and  the 
c  5 


50  WATER. 

board,  than  there  is  between  the  oil  and  the 
air." 

"  Will  anything  else  evaporate  besides 
water  ?  "  said  Rollo. 

"  Let  me  think,"  said  she.  "  There  is 
oil,  —  that  will  not.  What  other  liquids  are 
there  ? " 

"  Milk,"  said  Rollo. 

"  Milk  contains  a  great  deal  of  water ;  I  be- 
lieve a  large  part  of  its  substance  is  of  watery 
particles,  and  these  will  evaporate,  leaving  the 
rest.  It  is  generally  the  case  that  when  water 
has  anything  mixed  with  it,  or  dissolved  in  it, 
if  you  expose  it  to  the  air,  the  water  will 
evaporate,  and  leave  the  other  substances 
dry." 

"  There  is  ink,"  said  Rollo. 

"  Yes,"  said  his  mother,  "  that  is  a  very 
good  example.  It  consists,  you  see,  of  a  blacR 
coloring  matter,  dissolved  in  water ;  and  the 
water  will  evaporate,  and  leave  all  the  black 
part  behind,  on  the  paper." 

"  Then,  it  seems,  nothing  will  dry  up  but 
water,"  said  Rollo. 

"  I  don't  think  of  anything." 

"  Then  I  have  learned  one  thing,  haven't 
I?  "said  he. 

"  No,  you  have  not  learned  yet  that  nothing 


THE    THREE    DIFFICULTIES.  51 

will  evaporate  but  water,  from  such  reasoning 
as  this.  It  would  be  very  poor  induction." 

"  Induction  ?  "  said  Rollo.  "  What  is  in- 
duction 1 " 

"  Why,  when  we  say  a  thing  is  always  true, 
because  it  is  true  in  all  the  cases  we  have 
known,  that  is  induction." 

"  Is  that  a  good  argument  ?  "  said  Rollo. 

"  Yes,  sometimes  ;  but  we  cannot  establish 
a  general  truth  in  that  way,  unless  we  have 
taken  a  great  deal  of  pains  to  get  all  the  facts 
we  can  possibly  collect.  It  would  not  be  safe 
at  all  for  us  to  judge  from  the  very  few  liquids 
that  we  happen  to  think  of  just  now.  Boys 
are  very  apt  to  make  false  inductions." 

"  How  ?  "  said  Rollo. 

"  O,  in  a  thousand  ways.  Once  I  took  you 
out  in  the  fields  to  get  some  strawberries.  1 
told  you  I  knew  a  place  where  they  were 
very  thick  and  large.  You  went  with  me, 
and,  as  soon  as  we  got  into  the  field  a  little 
way,  and  you  happened,  for  a  few  moments, 
at  first,  to  find  them  few  and  small,  you  said, 
'  O  mother,  this  isn't  a  good  field  at  all.'  " 

"  Was  that  false  induction  ?  "  said  Rollo 

"  Yes :  from  a  very  few  particulars,  you 
came  to  a  general  conclusion,  and  your  con- 
clusion was  wrong  ;  for  we  afterwards  found 


52  WATER 

them  very  large  and  very  plentiful.  To  have 
made  a  sound  induction,  you  ought  to  have 
waited  till  you  had  gone  over  the  field  in  va- 
rious directions  ;  and  if  you  found  them  few 
and  small  wherever  you  went,  then  you  might 
properly  have  supposed  it  to  have  been  a  poor 
field  for  strawberries." 

"  Why,  then,  mother,  I  should  have  known ; 
for  1  should  have  seen  the  field  all  over." 

"  No,  you  would,  m  fact,  have  actually  seen 
only  a  small  part  of  all  the  strawberries,  and 
places  for  strawberries,  in  the  whole  field. 
But,  after  seeing  a  considerable  part  of  it,  you 
might,  perhaps,  have  safely  inferred  that  the 
rest  would  correspond.  This  would  have 
been  induction,  that  is,  inferring  a  general 
conclusion  from  a  knowledge  of  a  small  num- 
ber of  particulars." 

"  But  I  should  not  be  perfectly  sure." 

"  No,  we  can  never  be  perfectly  sure  in  in- 
duction, even  when  we  are  most  careful  and 
cautious,  and  therefore  we  must  take  great 
pains  not  to  judge  hastily.  There  is  no  way 
by  which  people  make  more  mistakes  than  by 
coming  to  general  conclusions  from  too  small 
a  number  of  facts.  But  we  are  getting  away 
from  evaporation.  Let  us  see  ;  where  did  we 
leave  off?" 


THE    THREE     DIFFICULTIES.  53 

Rollo  did  not  remember  exactly,  and  so 
nis  mother  began  anew  upon  another  part  of 
the  subject.  It  was  very  well  that  she  did 
not  allow  him  to  come  to  the  conclusion  that 
no  liquids  could  be  evaporated  except  water, 
just  because  the  few  that  he  happened  to  think 
of  could  not ;  for  there  are  several  liquids, 
entirely  different  from  water,  which  evapo- 
rate, and  some  of  them  more  rapidly  and 
readily  than  water  itself. 


Q,U  E  S  T  I  O  N  S  . 

What  was  Hollo's  boast  when  he  saw  Jonas  ?  Did  he 
really  know  all  about  water?  Did  he  even  know  all  about 
cohesion?  Which  do  you  think  knew  most  about  these 
subjects,  Rollo  or  Jonas  ?  What  was  the  first  question 
which  Jonas  proposed  ?  What  did  Rollo  say  to  this  ? 
What  was  the  second  question  ?  What  did  Rollo  say  to 
this?  Was  he  correct?  What  was  the  third  question ? 
Had  Rollo  ever  observed  these  globules  of  water?  How 
did  Jonas  know  that  they  were  not  bubbles  ?  Did  he  suc- 
ceed in  producing  them,  so  as  to  show  them  to  Rollo  ? 
How  many  of  these  questions  did  Rollo's  mother  under- 
take to  answer  ?  What  was  her  explanation  ?  Did  they 
think  of  any  other  liquid  besides  water  which  would  evapo- 
rate? What  did  she  say  about  the  evaporation  of  inkf 
Will  oil  evaporate  ?  Are  there  any  other  liquids  entirelj 
different  from  water  which  will  evaporate  ? 

5* 


CHAPTER    IV 

EVAPORATION. 

"  THERE  are  several  circumstances,"  said 
Rollo's  mother,  in  continuing  the  conversa- 
tion, "  which  make  the  air  take  up  water 
faster  than  it  otherwise  would,  or  which  pro- 
mote evaporation,  as  the  philosophers  call  it. 
One  is  warmth.  If  you  warm  a  board  or  pa- 
per that  is  wet,  or  warm  the  air  which  lies 
over  it,  the  moisture  will  evaporate  much 
quicker.  That  is  the  reason  why,  when  we 
want  anything  to  dry  quick,  we  hold  it  to 
the  fire." 

"  Is  it  ? "  said  Hollo. 

"Yes,"  said  his  mother.  "Air  can  only 
hold  a  certain  quantity  of  moisture,  though 
warm  air  can  hold  more  than  cold.  So,  if  we 
want  air  to  take  up  as  much  water  as  possi- 
ble, and  as  fast  as  possible,  we  must  warm 
it,  Then,  if  we  allow  this  warm  air  to  take 
up  as  much  water  as  it  will  hold,  and  after* 
wards  cool  it,  there  will  be  more  in  it  than  it 
xvill  hold." 


EVAPORATION.  5,* 

"  And  what  becomes  of  the  —  the — rest  ? ' 

"  The  surplus  ?  "  asked  his  mother. 

"Yes,  the  surplus." 

"  Why,  that  falls  down  out  of  the  air  again 
in  drops, — large  or  small  drops.  That  is 
the  way  that  it  comes  to  rain.  The  warm 
air,  in  the  long  summer  days,  lies  over  the 
sea,  and  ponds,  and  rivers,  and  takes  up  wa- 
ter, as  much,  perhaps,  or  nearly  as  much,  as 
the  warm  air  can  hold.  This  air  then  rises 
up  where  it  is  colder,  or  is  moved  in  winds, 
off  to  the  north,  and  thus  gets  cooled,  and 
then  it  can  no  longer  hold  the  moisture  it 
contains ;  and  so  it  falls  down  in  drops  of  rain, 
or  in  hail,  or  in  snow." 

"  Is  that  the  way  ?  "  said  Hollo. 

"  Yes,"  replied  his  mother.  "  There  is 
a  phenomenon  which  takes  place  in  houses, 
in  the  winter,  which  is  just  like  this,  in  prin- 
ciple. In  the  daytime,  when  the  room  is  ^ 
warm,  the  air  takes  up  moisture  from  our 
breaths,  and  from  various  other  sources,  until 
it  has  more  than  cold  air  can  contain.  Then, 
in  the  night,  the  cold  air,  outside  of  the  win- 
dows, cools  the  glass,  and,  through  the  glass, 
the  aii  in  the  room  which  touches  the  glass ; 
and  so  the  moisture  leaves  the  air,  and  at- 


56  WATER. 

laches  itself  to  the  glass,  and  makes  the 
beautiful  frost-work  you  have  seen  so  often. 

"  So,  with  our  breaths,  in  a  cold,  frosty 
morning,"  she  continued,  "the  air  which 
we  breathe,  when  it  conies  up  from  the  lungs, 
is  warm,  and  takes  up  a  great  deal  of  mois- 
ture from  all  the  passages  which  it  comes 
through.  Then,  when  it  comes  out  into  the 
cold,  it  is  suddenly  cooled,  and  cannot  hold 
so  much ;  and  so  the  surplus  becomes  visible 
in  little  drops." 

"  Little  drops  ?  "  said  Rollo. 

"  Yes,"  said  she.  "  That  vapory  appear- 
ance we  see  in  a  cold  morning,  like  a  little 
fog,  is  formed  of  little  drops  of  water,  too 
small  for  us  to  distinguish  one  by  one,  though 
all  together  they  make  a  sort  of  haze.  But 
it  vanishes  pretty  quick." 

"  What  makes  the  little  drops  vanish  ? " 
asked  Rollo. 

"Why,  they  spread  about  in  the  other 
air,  and  are  redissolved ;  that  is,  the  particles 
that  compose  them  are  taken  up  again  by  the 
air,  and  so  they  disappear." 

"  That's  curious,"  said  Rollo. 

"  I  think  it  is  very  curious/'  said  his 
mother. 


EVAPORATION.  57 

"  The  evaporation  of  water  is  going  on  al1 
the  time,"  she  continued,  "  from  all  ponds, 
and  lakes,  and  seas,  and  rivers — from  the 
ground,  the  leaves  of  trees,  the  brooks  —  from 
all  vessels  of  water,  or  watery  liquids  —  and 
from  all  wet  things,  of  every  kind ;  and  thus 
the  air  is  continually  receiving  new  supplies. 

"  Then  there  is  another  way  by  which 
water  is  turned  into  vapor,  besides  being  ta- 
ken up  by  the  atmosphere ;  that  is,  by  boiling 
it,  and  thus  changing  it  into  steam." 

"  I  have  seen  steam  coming  out  of  the 
nose  of  the  tea-kettle,"  said  Hollo. 

"  What  you  saw  is  not  strictly  steam,"  said 
his  mother,  "  though  it  is  commonly  called 
so.  Real  steam  is  invisible." 

"  Is  it  ?  "  said  Hollo. 

"Yes,"  said  his  mother.  "If  you  heat 
water  very  hot  indeed,  it  turns  into  a  kind 
of  hot,  scalding  air,  which  is  called  steam. 
This  steam  is,  in  fact,  water,  spread  out,  as 
it  were,  very  thin,  and  pressing  out  in  every 
direction,  just  like  air,  only  it  is  all  composed 
of  particles  of  water ;  and  as  soon  as  you  let 
it  cool,  it  turns  back  to  water  again.  So. 
you  see,  there  are  two  ways  of  getting  water 
off  from  an  iron  which  is  wet  with  it.  The 


58  WATER. 

first  way  is,  to  leave  the  iron  out  in  the  air 
and  the  air  will  gradually  take  all  the  watei 
up,  by  its  attraction  for  it ;  and,  if  you  warm 
the  iron  or  the  air  a  little,  it  will  take  it  up 
all  the  faster.  But  the  second  way  is,  to  put 
the  iron  over  the  fire,  and  heat  it  very  hot 
indeed ;  then  the  water  will  turn  at  once  in- 
to steam,  and  it  would  go  off  from  the  iron 
whether  there  was  any  air  over  it  or  not.  In 
fact,  if  there  is  a  good  deal  of  water,  the 
steam  will  push  the  air  away,  and  rise  up  in 
its  place." 

"  And  what  becomes  of  the  steam,"  said 
Rollo,  "  after  it  goes  away  from  the  iron  ?  " 

"  Why,  as  soon  as  it  should  get  away  from 
the  hot  iron,  and  mix  a  little  with  the  other 
air,  it  would  cool,  and  turn  into  little  drops 
of  water  again,  which  would  make  a  little 
white  cloud.  That  is  the  way  when  a  tea- 
kettle is  boiling.  The  fire  below  heats  the 
bottom  of  the  kettle  so  hot,  that  the  water 
next  to  it  turns  into  steam.  This  steam  now 
is  a  great  deal  lighter  than  the  water ;  and  so 
it  rises  up  through  it,  in  great  bubbles.  If 
the  fire  is  very  hot,  these  bubbles  of  steam 
come  up  very  fast,  and  make  the  boiling  noise 
that  we  hear.  This  bubbling  and  boiling  is 


EVAPORATION.  59 

because  the  fire  is  under  the  kettle,  and,  con- 
sequentlyf  the  bubbles  of  steam  are  formed  at 
the  bottom,  and  have  to  rise  up  through  the 
water.  If  the  heat  were  to  come  only  upon 
the  top  of  the  water,  I  suppose  there  would 
be  no  bubbling ;  for  the  steam  would  be  formed 
there,  and  would  pass  off  at  once,  silently, 
without  bubbling  through  the  water  at  all. 

"  Now,  when  these  bubbles  come  up  to  the 
upper  part  of  the  kettle,  they  fill  the  whole 
space  above  the  water  with  steam ;  and,  if 
you  could  peep  in  there,  you  would  see 
that  there  was  no  cloudy  appearance  of  va- 
por there  ;  it  would  be  pure  and  transparent, 
like  air." 

"  Did  you  ever  peep  in,  mother  ?  "  said 
Hollo. 

"  No,"  said  she. 

"  Then  how  do  you  know,  mother,"  asked 
Rollo,  "  if  you  never  looked  ? " 

"Because  I  have  seen  water  boiled  in  a 
glass  flask ;  and  then  I  could  see  through  the 
sides  of  the  fiask,  and  it  was  all  perfectly 
transparent  and  colorless ;  though,  as  soon  as 
the  steam  came  out  of  the  top,  into  the  cool 
air,  it  turned  into  a  column  of  visible  vapor. 
Besides,  if  you  look  into  the  nose  of  the  tea- 


bO  WATER. 

kettle,  you  will  see  that  there  is  no  appearance 
of  any  cloudiness  within  ;  nor  even  without, 
until  the  steam  has  got  away  a  little  dis- 
tance from  the  hot  iron,  so  as  to  be  cooled  a 
little.  You  can  see  it,  too,  in  chimneys, 
where  wood  is  burning,  or  any  other  fuel 
which  contains  moisture.  In  a  cold  morning. 
a  cloud  of  steam,  as  it  is  generally  called, 
comes  out  from  the  top ;  but  it  does  not  be- 
gin to  show  itself  until  it  has  got  up  a  foot 
or  two  above  the  top  of  the  chimney ;  foi 
it  comes  out  so  hot,  that  it  must  proceed  a 
little  way  into  the  air  to  get  cool  enough  tc 
turn  back  into  water  again,  or,  as  they  call  it, 
to  be  condensed. 

"  So,  you  see,  there  are  two  ways  by  which 
water  may  be  carried  off  into  the  air.  One 
is,  by  boiling  it,  and  turning  it  into  steam ; 
and  in  this  case  it  goes  off  in  a  mass,  which 
is,  ;n  fact,  all  water,  though  it  appears  like 
air.  The  other  way  is,  to  let  the  air  grad- 
ually take  it  up,  by  its  attraction ;  and,  in 
this  case,  it  mingles  with  the  air,  and  floats 
away.  And  when  steam  goes  up  into  the 
nir,  it  almost  immediately  becomes  condensed 
into  a  cloud  of  very  small,  watery  globules,  and 
these  are  then  gradually  dissolved  by  the  ais. 


EVAPORATION.  Cl 

"  If  it  were  not  for  these  modes  by  which 
water  is  carried  up  and  diffused  through  the 
air,  the  world  would  soon  be  in  a  sad  con- 
dition/' 

"  Would  it  ?  "  said  Rollo. 

"Yes.  I  think  the  consequences  would 
be  as  dreadful  as  those  your  father  said  we 
should  suffer  if  water  were  to  be  deprived  of 
its  adhesive  and  cohesive  properties." 

"  What  would  the  consequences  be  ? " 
asked  Rollo. 

"  Why,  in  the  first  place,  if  anything  was 
once  wet,  we  could  never  dry  it." 

"  Couldn't  we,  possibly,"  said  Rollo,  "  in 
any  way  ? " 

I'  It  would  be  very  difficult,"  said  his  moth- 
er. "It  would  be  something  as  it  is  now 
with  oil.  If  we  get  oil  upon  our  clothes  or 
hands,  or  upon  a  board,  it  is  very  difficult  to 
get  it  out.  The  reason  is,  the  atmosphere 
will  not  take  it  up.  And  we  cannot  easily 
contrive  any  way  to  remove  it.  If  the  air 
would  not  take  up  water,  then,  whenever  we 
should  wet  our  hands,  they  would  have  to 
remain  wet.  And  every  thing  else  which 
we  might  touch  would  be  wet.  There 
would  be  no  such  thing  as  drying  anything. 
6 


62  WATER. 

"  Then,  again,  the  ground  would  be  per- 
manently wet  and  muddy.  For,  if  the  at- 
mosphere had  no  attraction  for  water,  all  the 
water  which  is  now  in  the  atmosphere  would 
fall  at  once,  and  flood  the  ground.  A  great 
part  of  this  would  run  off  into  the  rivers  and 
into  the  sea ;  but  enough  would  be  retained 
by  the  attraction  of  cohesion  to  make  every- 
thing wet  and  disagreeable.  It  would  be  as 
if  it  should  rain  oil  until  everything  was 
drenched  with  it ;  and  then  a  large  portion 
might  run  off,  but  still  it  would  leave  every- 
thing soaked  with  oil,  never  more  to  be  dry. 

"  And  then  we  could  never  have  any  more 
rain.  For  after  the  water,  which  is  now  in 
the  atmosphere,  had  fallen  down,  no  more 
could  ever  get  up ;  and.  of  cpurse,  we  should 
never  have  any  more  clouds  or  rain.  The 
streams,  of  every  kind,  would  soon  all  run 
off  in  the  sea,  leaving  their  bottoms  forever 
muddy ;  and  then  everything  would  continue 
wet,  wet  everywhere  and  perpetually.  So 
you  see,  Hollo,  how  nicely  the  properties  of 
water  have  been  arranged  to  make  this  w  orld 
a  pleasant  place  for  us  to  live  in." 

Here  Hollo's  mother  put  away  her  work, 
and  said  that  she  could  not  talk  with  him  any 


EVAPORATION.  63 

longer ;  and  he  went  out  to  find  Jonas,  to  tell 
him  what  he  had  learned  in  answer  to  his 
second  question. 

Rollo  met  Jonas  going  into  the  garden  to 
his  work,  and  Jonas  asked  him  to  go  out  with 
him,  for  he  wanted  to  talk  with  him  a  little. 
While  Jonas  was  at  his  work  hoeing,  he  told 
Rollo  that  he  had  thought  of  an  experiment 
to  prove  to  him  that  water  does  not  all 
dry  up  "  to  nothing,"  as  Rollo  had  thought. 

"  0,  I  know  it  does  not,  now,"  said  Rollo ; 
"  mother  has  explained  it  to  me.  It  goes  off 
into  the  air,  in  very  fine,  invisible  particles. 
But  what  was  your  experiment  ?  " 

"  Will  you  try  it,"  said  Jonas,  "  if  I  will 
explain  it  to  you  ?  " 

"  Yes,"  said  Rollo,  "  if  I  can." 

"  Very  well ;  first  you  must  go  into  the 
house,  and  get  a  phial." 

"  What  kind  of  a  phial  ?  "  said  Rollo. 

"  O,  any  kind  of  small  phial ;  you  had 
better  get  one  out  of  the  medicine  closet,  that 
is  about  empty,  and  ought  to  be  washed  out, 
and  carry  it  to  the  pump,  and  wash  it  out 
clean,  and  then  bring  it  to  me." 

So  Rollo  went,  and  asked  his  mother  to 
give  him  such  a  phial ;  and  she  did  so.  Rol- 


64  WATER. 

lo  brought  it  to  the  pump,  and  tried  to  pump 
water  into  it,  but  the  water  would  not  go 
in.  It  poured  down  in  torrents  all  over  the 
sides  of  it,  but  very  little  would  go  in.  He, 
however,  at  length  succeeded  in  getting  in  as 
much  as  was  necessary  for  washing  out  the 
phial ;  then  he  carried  it  to  Jonas,  to  ask  him 
what  the  experiment  was. 

Jonas  took  the  phial  into  his  hands,  and 
examined  it. 

"  There,  you  see,"  said  he,  "  there  are 
some  drops  of  water  on  the  inside  of  the 
glass,  and  some  on  the  outside.  Now,  put 
the  cork  in,  and  go  and  put  the  phial  down  in 
the  sun.  Then,  in  about  an  hour,  go  and 
look  at  it  again.  Now,  if  the  warmth  of  the 
sun  makes  the  water  go  all  '  to  nothing,'  the 
glass  will  be  dry,  inside  and  out ;  but  if  the 
water  all  goes  away,  when  it  dries  up,  then 
the  outside  will  dry,  but  the  inside  will  not, 
for  the  water  that  is  inside  cannot  get  away." 

"Yes,"  said  Rollo,  "that  will  prove  it. 
I  will  go  and  put  it  in  a  good  place." 

Rollo  accordingly  put  it  in  a  corner  of  the 
yard  where  the  sun  shone  very  warm,  and 
then  went  away  to  play.  He  did  not  think 
of  the  phial  again  until  the  next  morning ; 


EVAPORATION.  65 

and  then,  when  he  and  Jonas  went  to  look 
at  it,  they  found  that  it  was  perfectly  dry 
outside,  but  inside  there  was  a  sort  of  dew 
upon  the  glass,  and  some  drops  of  water  li- 
the bottom.  So  they  considered  it  estab 
lished  that  water,  in  drying  up,  did  not  gf 
"all  to  nothing." 


QUESTIONS. 

What  is  the  meaning  of  the  expression  "  promote  evapo- 
ration "  ?  What  is  it  that  Hollo's  mother  said  did  promote 
evaporation?  Which  can  hold  the  greatest  quantity  of 
water,  warm  air  or  cold .'  When  warm  air  has  taken  up 
all  that  it  can,  and  afterwards  becomes  cold,  what  hap- 
pens ?  Is  true  steam  visible  or  invisible  ?  Is  not  what 
is  often  called  steam  visible  ?  How  does  it  look  ?  What 
does  it  really  consist  of?  What  proof  did  Hollo's  mother 
offer  that  true  steam  was  not  visible  ?  What  would  be 
some  of  the  consequences  if  water  did  not  possess  the 
property  of  being  dissolved  by  the  air  ?  What  was  Jo  las's 
experiment?  What  did  he  intend  to  prove  by  it?  Did 
it  succeed  to  Hollo's  satisfaction  f 

c*  6* 


CHAPTER    V. 

DAM   BUILDING. 

ONE  day.  Hollo's  cousin  James  came  to  see 
him,  and  he  and  Hollo  concluded  to  go  down 
into  the  woods  behind  the  house  to  play. 
They  came  to  the  great  brook,  and  amused 
themselves  for  some  time  in  looking  into  the 
deep  places,  to  see  if  they  could  find  any 
fishes. 

It  was  midsummer,  and  the  brook  was 
very  low.  Rollo  said  that  he  wished  that 
there  was  as  much  water  in  the  brook  as 
there  had  been  early  in  the  spring. 

"  Then,  James,"  said  he,  "  it  was  almost 
full,  up  even  with  the  banks ;  but  now  there 
is  only  a  little  stream  running  over  the  peb- 
ble s-tones  from  one  deep  place  to  another." 

"  Let  us  build  a  dam,  then,"  said  James ; 
'that  will  make  it  deep." 

"  O,  so  we  will,"  said  Rollo.  "  We  can 
build  it  of  sods.  We  will  go  up  and  get  my 
littlr  spade  to  cut  some  sods  wifh." 


DAM    BUILDING.  67 

Sc  the  boys  sauntered  along  home  to  get 
the  spade.  They  found  it  in  its  place,  for 
Rollo  was  always  very  careful  to  put  it  where 
it  belonged.  James  saw  Hollo's  little  wheel- 
barrow in  the  shed  while  Rollo  was  getting 
his  spade,  and  he  proposed  that  they  should 
take  that  down  too.  "Because,"  said  he, 
"  you  know,  Rollo,  we  may  want  to  bring 
our  sods  some  distance." 

So  the  boys  put  the  spade  into  the  wheel- 
barrow, and  trundled  it  down  to  the  brook. 
They  moved  so  slowly,  and  stopped  so  often 
to  talk  about  what  they  saw  by  the  side  of 
the  path,  that  it  was  nearly  half  an  hour  be- 
fore they  got  back  to  the  brook ;  and  then, 
just  as  they  were  beginning  to  dig  their  first 
sod,  they  heard  a  noise  like  some  one  calling 
out  to  oxen,  in  the  woods  beyond  them. 

"  What  is  that  ? "  said  James. 

"  O,  it  is  only  Jonas,"  said  Rollo. 

"  I  wish  he  would  come  here,"  said  James, 
"  and  just  show  us  how  to  build  our  dam." 

"  He  is  coming  right  along  here,"  replied 
Rollo ;  "  see,  there  is  where  he  crosses  the 
brook." 

So  saying,  Rollo  pointed  down  a  little  be- 
low them,  and  James  saw  a  smooth,  shallow 


68  WATER. 

place  in  the  brook,  where  the  bottom  consist- 
ed of  sand  and  gravel,  and  a  cart  path  led 
down  into  it  from  the  bank  on  both  sides. 

"  That  is  Jonas's  ford,"  said  Rollo. 

"  Ford  ?  "  said  James ;  "  what  is  a  ford  ?  " 

"  O,  it  is  such  a  place  as  that,  where  horses 
and  teams  can  walk  across  a  brook.  Only  in 
rivers,  at  a  ford,  the  water  is  a  great  deal 
deeper.  Jonas  went  across  a  ford  on  a  horse 
once,  where  the  water  was  up  so  high  that 
he  had  to  lift  up  his  feet  to  kee'p  them  out 
of  it." 

"  O  Rollo  !  "  said  James,  incredulously. 

"  He  did,"  said  Rollo.  "  He  told  me  so. 
But  this  ford  is  very  shallow,  —  though  it  is 
pretty  deep  in  the  spring,  when  the  water  is 
high.  Jonas  made  the  ford  on  purpose  for 
his  cart  to  go  through." 

By  this  time,  the  horns  of  Jonas's  oxen, 
and  presently  Jonas  himself,  and  a  cart, 
loaded  with  small  sticks  of  wood,  began  to 
appear  through  the  bushes.  The  cattle  came 
down  to  the  ford,  and  stopped  upon  the  sandy 
bed  of  the  brook  to  drink.  Jonas  walked 
over  the  brook  upon  a  log  which  he  had 
drawn  across  it  just  above  the  ford,  for  a 
bridge.  He  left  the  oxen  in  the  brook,  and 


'THAT  IS  JOXAS'S  FORD,"  SAID  HOLLO.     Page  68. 


DAM    BUILDING.  69 

walked  up  the  bank  to  where  Rollo  and 
James  were  at  work,  and  asked  them  what 
they  were  doing. 

"  O,  we  are  building  a  dam,"  said  Rollo. 

Jonas  smiled. 

"  Now,  what  are  you  laughing  at,  Jonas  ?  " 
said  Rollo. 

"  Why,  nothing,  —  only  your  dams  and 
bridges  are  very  apt  to  go  down  stream." 

"  But  this  will  not,"  said  James,  "  for  we 
are  going  to  make  it  of  sods,  —  good,  heavy 
sods." 

The  boys  had  some  further  conversation 
on  the  subject ;  and  at  length  Rollo  said  that 
one  reason  why  he  was  going  to  build  a  dam, 
was  to  make  an  experiment  on  the  philosophy 
of  water.  He  said  that  his  mother  had  given 
him  a  book  where  he  had  read  something 
about  running  water,  and  now  he  was  going 
to  try  some  experiments. 

"  There  will  be  two  conflicting  principles, 
you  see,  Jonas,"  said  Rollo,  very  gravely,  re- 
peating what  he  remembered  to  have  read  in 
his  book.  "  First,  the  gravitation  of  the  wa- 
ter, tending  to  carry  it  down  ;  and,  secondly, 
the  resistance  of  the  dam,  tending  to  keep  il 
back." 


70 


WATER. 


Just  at  this  time  the  boys  heard  a  rustling 
among  the  dry  leaves  near  them,  and,  looking 
up,  they  saw  a  young  lady  coming  along  a 
path  under  some  trees,  towards  them.  It 
was  Miss  Mary,  their  old  school-teacher. 

Miss  Mary  paused  a  moment  upon  the 
bank,  and  then  said,  — 

"  There  are  two  other  conflicting  princi- 
ples, that  I  think  it  more  likely  you  will  il- 
lustrate," said  she. 

"  What  are  they  ?  "  said  Rollo. 

"  Why,  the  first,"  rejoined  Miss  Mary,  "  is 
the  desire  of  all  boys  to  play  in  mud  and 
water  ;  and,  secondly,  the  desire  of  all  mothers 
to  keep  them  away  from  it." 

"  O  Miss  Mary,"  said  James,  "  there  is  not 
any  mud." 

"No,"  said  Rollo,  —  "only  water, — and 
clean  sand  and  gravel.  Besides,  I  am  very 
careful  not  to  get  wet  and  muddy  about  the 
brook.  See !  " 

So  Rollo  pointed  down  to  his  shoes,  and 
Miss  Mary  saw  that  they  were  clean  and  dry. 
In  fact,  Rollo  and  James  both  had  more  sense 
than  most  boys  have,  in  respect  to  playing  in 
the  water,  as  they  always  took  special  paim 
to  prevent  getting  their  shoes  or  clothes  wel 


DAM    BUILDING.  71 

and  muddy  ;  for  Rollo  had  observed  that  this 
always  gave  his  mother  a  great  deal  of  trouble, 
and  prevented  her  allowing  him  to  go  near 
the  water  the  next  time. 

After  some  further  conversation,  Jonas  said 
that  the  neatest  way  to  make  their  dam  was 
to  make  it  of  a  wide  board,  just  long  enough 
to  reach  from  bank  to  bank ;  and  he  ex- 
plained to  them  fully  how  to  do  it,  supporting 
it  with  stakes  on  the  lower  side,  and  drawing 
gravel  against  the  lower  edge  and  the  ends 
of  the  board,  upon  the  upper  side,  to  make 
it  tight. 

"  And  where  shall  we  get  our  board  ?  "  said 
Rollo. 

"  I  will  get  one  out  for  you  at  the  house, 
when  I  go  up,"  said  Jonas. 

"And  bring  it  down  with  you  on  the 
cart?"  asked  Rollo. 

"  Yes,"  said  Jonas.  "  And  you  and  James 
may  ride  up,  too,  if  you  wish." 

"  Well ! "  said  Rollo  and  James,  with  a 
tone  of  great  satisfaction ;  and  they  laid 
down  their  spade,  and  ran  towards  the  ford, 
and  across  the  log,  so  as  to  get  into  the  cart ; 
for,  as  the  oxen  were  standing  in  the  brook, 
the  tail  of  the  cart  was  so  near  the  farther 


72  WATER. 

bank  that  they  could  climb  in.  It  was  not  a 
large  load  of  Avood,  and  Hollo  and  James 
clambered  up  to  the  top  of  it. 

"  We  shall  have  a  ride  through  the  brook,' 
said  James. 

"  Yes,"  said  Rollo  ;  "  and  see  Jonas.  He's 
measuring." 

James  looked,  and  saw  that  Jonas  was 
measuring  the  breadth  of  the  brook  from 
bank  to  bank,  at  the  place  where  they  were 
going  to  make  their  dam.  These  banks 
were  about  a  foot  and  a  half  high,  and  were 
nearly  perpendicular,  and  formed  of  a  sort  of 
green  moss,  which  covered  and  concealed  the 
earth.  Jonas  measured  from  one  of  these 
banks  to  the  other,  with  his  goad  stick,  so 
that  he  might  make  the  board  of  the  right 
length. 

Then  he  came  down  to  the  ford,  and  spoke 
to  his  oxen,  and  they,  obedient  to  his  com- 
mand, began  slowly  to  move  up  the  slope, 
which  led  from  the  bed  of  the  brook  where 
they  had  been  standing.  Rollo  and  James 
sat  on  the  top,  upon  the  wood.  As  they 
rode  slowly  along  the  cart  road,  towards  the 
house,  they  saw  Miss  Mary  just  disappearing 
by  a  narrow  footpath  which  led  through  the 


DAM    BUILDING.  73 

tliickot  in  another  direction.  Rollo  called 
out  to  her  to  come  back  by  and  by,  and  see 
their  dam.  Miss  Mary  said  that  she  would, 
and  that,  if  it  worked  well,  she  would  give 
them  a  lecture  upon  philosophy,  by  the  help 
of  it. 

When  they  reached  the  house,  Jonas  threw 
off  his  load  of  wood,  and  then  went  with  the 
boys  to  find  a  board.  He  took  a  pretty  wide 
one  from  a  pile  of  boards  and  other  lumber 
which  Avas  in  a  corner  of  the  yard,  and,  after 
carefully  measuring  a  certain  portion  of  it 
with  his  goad  stick,  he  sawed  it  off,  and 
then  took  it  under  his  arm,  and  carried  it  to 
the  cart.  He  then  went  off  towards  the 
barn. 

"  Where  now,  Jonas  ?  "  asked  Rollo. 

"I  am  going  after  an  auger,"  said  Jo- 
nas. 

"  An  auger,"  exclaimed  Rollo,  "  what  is 
that  for?" 

"  You'll  see,"  said  Jonas. 

Presently  Jonas  appeared  again,  coming 
out  of  the  tool-room  door,  with  two  augers 
in  his  hand.  He  came  to  the  board,  and 
began  to  bore  a  hole  with  the  large  auger 
very  near  the  middle  of  it. 
d  7 


T4  WATER. 

"  Why,  Jonas,"  said  James,  "  you'll  spoil  the 
dam.  That  hole  will  let  the  water  all  run 
through." 

"  But  I'm  going  to  make  a  plug  to  stop  it 
up,"  said  Jonas. 

"  O."'  said  James. 

"  Seems  to  me  that  is  not  very  wise,"  said 
Hollo  —  "to  make  a  hole,  just  for  the  sake  of 
making  a  plug  to  stop  it  up  with." 

Jonas  said  nothing,  but  went  on  boring 
his  hole.  After  he  had  finished  it,  he  took 
the  small  auger,  and  bored  two  small  holes 
with  it  by  the  side  of  the  great  one.  These 
two  small  holes  were  bored  in  such  a  way 
that,  when  the  board  was  afterwards  placed 
upright  upon  its  edge  across  the  bed  of  the 
brook,  one  of  them  was  directly  over  the 
other, — the  lower  one  being  pretty  near  the 
lower  edge  of  the  board,  and  the  upper  one 
near  the  upper  edge.  He  also  made  three 
plugs  to  fit  the  three  holes. 

Jonas  then  put  the  two  augers  away,  and 
went  and  made  two  strong  stakes.  Then  he 
put  the  board,  and  the  stakes,  and  the  axe, 
into  the  cart,  and  told  the  boys  to  climb  in. 
This  the  boys  were  very  ready  to  do.  Jonas 
then  took  his  seat  upon  the  tongue,  before 


DAM   BUILDING.  75 

the  cart  body,  and  they  all  rode  off  towards 
the  brook  together. 

When  Jonas  came  to  lay  the  board  across 
the  brook  from  one  bank  to  the  other,  Hollo 
exclaimed,  — 

"  There  now,  Jonas,  you  have  got  it  too 
long  ;  I  thought  it  was  too  long." 

The  board  did,  in  fact,  extend  a  few  inches 
over  upon  the  green,  mossy  bank  on  each 
side.  Jonas,  however,  took  the  spade,  and  cut 
a  little  notch  or  groove  in  each  bank,  where 
the  ends  of  the  board  were  to  come,  and 
then  crowded  the  board  down  into  them. 
Thus  the  board  extended  into  the  bank  a 
little  on  each  side,  and  this  held  it  pretty 
firmly  in  its  place.  Then  Hollo  saw  that 
Jonas  had  not  made  a  mistake  in  his  measure. 

To  confine  the  board  still  more  securely  in 
its  position,  Jonas  next  drove  down  the  two 
stakes  behind  it,  into  the  bottom  of  the 
brook,  —  one  near  each  end.  Then,  with 
Hollo's  little  spade,  he  dug  a  little  trench  in 
the  sand  and  gravel,  exactly  under  the  low'er 
edge  of  the  board,  so  as  to  let  the  edge  go 
down  a  little  below  the  surface  of  the  sand 
and  gravel.  When  this  was  done,  he  drove 
the  board  down  into  it,*striking  it  gently 


76  WATER. 

upon  the  upper  edge,  in  several  places,  so  as 
to  settle  it  all  together.  When  it  was  settled 
down  well  into  its  place,  he  put  the  axe  upon 
his  shoulder,  and  said,  — 

"  There,  boys,  now  take  your  spade,  and 
bank  it  up  well  with  gravel  on  the  upper 
side,  and  see  if  it  will  hold  water." 

"  How  much  must  we  bank  it  up  ?  "  said 
Rollo,  calling  after  Jonas,  as  the  cattle  were 
just  going  through  the  ford. 

"  O,  the  more  the  better,"  said  Jonas.  "  If 
you  don't  bank  it  up  well,  it  will  blow" 

"  What  does  he  mean  by  blow  ? "  said 
James. 

"  I  don't  know,"  said  Rollo.  "  I'll  call  out 
and  ask  him.  — Jonas  !  Jonas !  what  do  you 
mean  by  blow  ?  " 

But  Jonas  was  too  far  gone  for  Rollo  to  get 
any  answer.  When  he  listened  for  a  reply, 
he  could  hear  nothing  but  the  distant  sound 
of  the  heavy  cart  wheels  upon  the  dry  brush, 
and  Jonas's  voice  calling  out  to  direct  the 
oxen. 

When  Rollo  and  James  turned  to  their 
dam,  they  found  that  the  water  was  slowly 
accumulating  upon  the  upper  side  of  it 

"  O,  look,"  said  Rollo  ;  "  the  water  is  dam- 


DAM    BUILDING.  77 

ming    up!    it  is  damming  up!      We  must 
shovel  the  gravel  on  quick." 

So  Rollo  stepped  down  upon  a  dry  sand- 
bank just  above  the  dam,  and  began  throwing 
sand,  and  gravel,  and  mud,  from  the  bottom, 
over  towards  the  board.  He  threw  it  against 
the  ends  of  the  board,  and  along  tb,e  lower 
edge,  so  as  to  stop  the  Joints,  as  he  called 
them.  James  stood  by,  looking  on,  and 
wishing  that  he  had  a  spade  too.  Presently, 
however,  Rollo  stopped  to  rest  and  let  James 
take  his  place ;  and  while  they  were  working 
busily  so,  Miss  Mary,  returning  from  her  walk| 
came  back  to  the  place  to  see  how  they  got 
along. 

Miss  Mary  told  James  that  his  feet  were 
getting  wet ;  and  James,  on  looking  down,  saw 
that  the  water  was  rising  over  the  sand-bank, 
and  spreading  all  around  his  fe§t.  So  James 
jumped  off  of  it  to  the  shore,  and  said  that 
then  they  could  not  shovel  on  any  more 
gravel. 

"  If  you  had  a  hoe,"  said  Miss  Mary,  "  you 
could  stand  down  below  the  dam,  and  hoe  it 
on ;  for  you  could  reach  with  your  hoe  down 
to  the  bottom  of  the  water." 

''Well,"  said    Rollo,  "let   us   go,  James 
7* 


78  WATER. 

and  get  some  hoes,  and  bank  it  up  a  great 
deal ;  for  we  don't  want  our  dam  to  blow." 

"  To  blow"  said  Miss  Mary ;  "  what  do  you 
mean  by  that  ?  " 

"  Why,  I  don't  know,  exactly,"  said  Rollo  ; 
"  only  Jolls  said  that,  unless  we  banked  it 
up  pretty  well,  it  would  blow." 

"I  presume  he  meant  that  it  would  leak," 
said  Miss  Mary. 

This  was  a  pretty  good  conjecture  at  the 
meaning  of  the  word,  but  it  was  not  exactly 
correct.  The  children  did  not  find  out  till 
Afterwards  what  it  was  that  Jonas  meant. 

Miss  Mary  told  them  that  it  was  better  to 
make  their  work  secure,  and  accordingly 
Rollo  went  up  to  the  house,  and  brought 
down  two  hoes,  one  for  himself  and  one  for 
Tames.  They  then  put  some  large  pieces  of 
decay4P  logs^^rhich  they  found  in  the  woods 
pretty  near,  in  the  bed  of  the  brook  below 
the  dam,  to  make  a  dry  place  to  stand  upon. 
Then,  standing  there,  they  reached  over  the 
board,  and  drew  the  sand  an4  gravel  from  the 
bed  of  the  brook  above  it  towards  the  dam, 
unti.  they  had  banked  it  up  very  nearly  as 
high  as  the  top  of  the  board.  In  the*mean 
f;me,  the  water  was  continually  rising,  until, 


DAM    BUILDING.  81 

at  length,  it  got  pretty  deep,  —  so  deep,  in 
fact,  that  they  could  not  draw  up^any  more 
gravel. 

"There,"  said  Hollo,  "it  makes  a<-very 
pretty  little  pond." 

"Yes,"  said  Miss  Mary,  "only* the  water 
is  very  muddy." 

"  0,  that  is  only  because  we  hoed  the  sand 
and  gravel  with  our  hoes,"  said  Roilo.  "  It 
will  soon  settle." 

The  children  sat  down  upon  the  bank  to 
watch  the  rising  of  the  water,  and  to  see  if 
it  would  not  become  more  clear;  but  it  did. 
not  become  clear  very  fast,  and  there  was  a 
sort  of  scum  of  dust,  leaves,  straws,  and  other 
light  substances,  which  the  water  had  taken 
up  from  the  surface  of  the  ground,  which  it 
gradually  covered,  as  it  had  risen  higher  and 
higher,  and  had  consequently  spread  q|it  over 
places  which  before  were  dry. 

At  length  Hollo,  as  if  suddenly  recollecting 
himself,  said,  — 

"  O  Miss  Maim  you  promised  to  deliver  us 
a  lecture." 

"Well,"  said  Miss  Mary,  "1  will  begin 
now." 


82  WATER. 

So  Hollo  and  James  sat  still  and  listened 
attentive!^  while  Miss  Mary  commenced  her 
lecture,  as  follows. 


QUESTIONS. 

What  was  the  state  of  the  brook  when  Hollo  and  Tam>8 
went  down  to  see  it?  What  season  of  the  year  was  it? 
Why  are  brooks  higher  in  spring  than  in  midsummer? 
What  is  a  ford  ?  Did  Jonas  have  much  confidence  that 
they  could  build  a  dam  that  would  stand  ?  What  difficulty 
did  he  seem  to  anticipate?  What  difficulty  did  Miss  Mary 
'.*seern  to  anticipate  ?  What  preparatory  step  did  Jonas  take 
before  he  left  the  brook  ?  Did  he  saw  off  the  board  so  as 
to  have  it  exactly  as  long  as  the  brook  was  wide  ?  Why 
did  he  make  it  a  little  longer?  How  many  holes  did  he 
bore  ?  How  were  the  holes  placed,  in  respc  ct  to  each 
other?  What  was  the  appearance  of  the  lit  k?  pond  of 
water,  when  it  was  completed  ? 


CHAPTER    VI. 

HYDRAULICS. 

"  WATER  is  a  fluid.  It  is  called  a  fluid 
because  the  parts  of  it  move  very  easily 
among  themselves.  All  substances  are  fluids 
if  their  parts  move  easily  among  themselves. 
So  milk  is  a  fluid,  and  vinegar  is  a  fluid,  and 
air  is  a  fluid.  But  wood  is  not  a  fluid,  for 
the  parts  or  particles  of  wood  do  not  move 
easily  among  themselves.  In  fact,  you  can- 
not move  them  among  themselves  at  all." 

"Why,  you  can  break  the  wood,"  said 
Hollo. 

"  Yes,"  replied  Miss  Mary,  "but  that  is  not 
moving  the  particles  among  themselves;  — 
it  is  separating  the  particles,  dividing  them 
moving  one  part  away  from  another,  but  not 
moving  them  among  themselves.  Now  you 
may  answer  some  questions. 

"  Is  iron  a  fluid  ?  " 

"  No,"  replied  Rollo  and  James  together. 

"  Is  brass  ?  " 


84  WATER. 

"No." 

"Is  sponge?" 

"Yes,  a  little,"  said  James. 

At  the  same  instant  that  James  was  saying 
yes,  Rollo  was  just  going  to  say  no ;  but  he 
was  not  quite  sure. 

"No,"  said  Miss  Mary,  "sponge  is  not 
fluid  at  all.  True,  you  can  press  the  parts 
together,  and  then  they  will  spread  open 
again;  but  they  do  not  move  at  all  among 
themselves.  But  there  are  substances  which 
are  a  little  fluid." 

"What?"  said  Rollo. 

"Pitch,  and  lava  from  burning  mountains, 
and  candy  before  it  is  cold.  The  particles 
of  all  these  will  move  about  among  them- 
selves, though  with  difficulty;  and  so  they 
are  called  semi-fluids,  that  is,  half  fluids  ;  for 
semi  means  half.  But  water  is  a  perfect 
fluid ;  for  the  particles  not  only  move  among 
themselves,  but  they  move  easily.  Do  you 
understand  all  that  ?  " 

"Yes,"  said  the  boys,  "all  that  is  very 
plain." 

"  Now,"  continued  Miss  Mary,  "  a  fluid  has 
several  very  remarkable  properties." 


HYDRAULICS.  85 

"  Proj  erties  ?  "  said  Rollo  ;  "  what  are  prop- 
erties ? " 

"  I  know,"  said  James ;  "  houses  and  land 
is  property." 

Here  Rollo  laughed  loud  and  long  at  James's 
idea  that  water  or  any  other  fluid  could  have 
property  in  such  a  sense  as  that ;  even  Miss 
Mary  smiled  a  little,  and  said  that  she  did 
not  mean  property  in  that  sense. 

"  Well,  what  kind  of  property,  then  ?  " 

"  Properties,  I  said,"  replied  Miss  Mary. 
"That  means  —  I  hardly  know  how  I  can 
explain  it  to  you,  now.  Properties  are,  —  are 
—  I  think,  now,  the  best  way  will  be  to  tell 
you  what  some  of  the  properties  of  a  fluid 
are,  and  then  you  will  see  for  yourself  what 
the  word  means." 

"  O,  I  remember,  now,"  said  Rollo ;  "  father 
explained  it  to  me  once." 

"  The  first  property  of  a  fluid,"  continued 
Miss  Mary,  without  replying  to  Rollo,  "  is 
that,  if  it  is  left  to  itself,  the  surface  of  it  be- 
comes level." 

"  Always  ?  "  asked  Rollo. 

"  Yes,  always,  I  believe,"  continued  Miss 
Mary.  "  The  surface  or  top  of  the  water  in  a 
bowl  will  always  be  exactly  level,  so  that,  if 
8 


86  WATER. 

the  bowl  were  to  stand  still,  and  the  wate: 
freeze,  a  ball  would  not  roll  upon  it  one  way 
any  easier  than  another.  So  the  water  in  a 
pond,  when  it  is  still,  will  always  be  exactly 
level.  And  the  water  in  the  sea  will  be 
level  except  when  the  wind,  or  some  other 
cause,  disturbs  it.  Now,  the  reason  why  it  is 
so,  is  this  :  As  the  particles  of  water  move 
very  easily  among  themselves,  if  one  part  of 
the  water  should,  by  any  accident,  be  higher 
than  the  rest,  it  would  move  and  settle  away 
by  its  weight  towards  the  lower  part,  and  thus 
make  it  level  again.  And  so,  you  see,  one 
of  the  properties  of  a  fluid  is,  that  its  surface 
is  always  level,  when  it  is  left  to  itself." 

"  Is  that  what  you  mean  by  property  ? " 
:-'aid  James. 

"  Yes,"  answered  Miss  Mary.  "  The  sur- 
face in  brooks  and  rivers  is  not  level,  be- 
cause water  is  continually  coming  in,  at 
one  extremity,  from  the  springs  among  the 
mountains,  and  going  out,  at  the  other,  into 
the  sea,  which  is  lower ;  so  that  the  Water, 
throughout  the  whole  course  of  the  stream, 
is  always  moving,  seeking  its  level.  The 
nearer  level  it  is  in  any  part  of  its  course,  the 
slower  it  moves ;  and  the  steeper  the  descent 


HYDRAULICS.  87 

is,  the  swifter  it  goes.  Consequently,  when- 
ever you  see  the  water  smooth  and  pretty 
nearly  still,  as  it  is  in  your  dam,  then  you 
may  know  that  the  surface  is  pretty  nearly 
level.  But  if  it  shoots  along  swiftly,  then 
you  may  know  that  the  surface  descends." 

"  Another  property  of  fluids,"  continued 
Miss  Mary,  "is,  that  they  press  in  all  direc- 
tions." 

"  What  do  you  mean  by  that  ?  "  said 
James. 

"  Why,  if  you  had  a  barrel  full  of  water 
here,  the  water  would  press  not  only  on  the 
bottom  of  the  barrel,  but  upon  the  sides ; 
and  so,  if  you  were  to  bore  a  hole  any  where, 
the  water  would  spout  out.  But  if  you  had 
a  mass  of  iron  or  of  wood  of  the  shape  of  the 
barrel,  that  would  not  press  anywhere  but 
downwards,  upon  the  floor,  or  upon  the 
ground,  whichever  it  might  stand  upon.  It 
would  press  very  heavily  upon  the  floor,  or 
the  ground,  but  it  would  not  press  outwards 
at  the  sides  at  all.  What  made  me  think  of 
this  principle,"  continued  Miss  Mary,  "was 
the  sight  of  your  plugs." 

"  How  did  that  make  you  think  of  it  ? " 
said  Rollo. 


88  WATER. 

"  Why,  the  water  in  your  dam,"  continued 
Miss  Mary,  "  not  only  presses  with  all  its 
weight  upon  the  sand  and  gravel  on  the  bot- 
tom, but  it  also  presses  outwards,  against  the 
dam ;  so  that,  if  you  pull  out  the  plug,  the 
water  will  spout  out." 

"  O  yes,"  said  Hollo ;  "  I  knew  that  be- 
fore." 

"  The  reason,"  continued  Miss  Mary,  "  why 
water  presses  outwards  as  well  as  down- 
wards, is,  that  the  particles  can  move  easily 
in  all  directions ;  and  so  the  water  which  is 
down  near  the  bottom  of  your  dam,  being 
pressed  by  the  weight  of  the  water  which  is 
above  it,  is  pressed  downwards  ;  but,  then,  if 
it  cannot  move  downwards,  on  account  of  the 
solid  bottom  of  sand  and  gravel,  it  will  slip 
out  to  one  side,  whenever  it  can  find  an 
opening.  This,  you  see,  is  because  the  par- 
ticles can  easily  move  among  themselves. 
But  the  particles  of  stone,  near  the  bottom  of 
a  large  mass  of  stone,  can  only  press  directly 
downwards ;  for  they  do  not  move  easily 
among  themselves,  and  so  cannot  move  out 
of  the  way." 

"  I  mean  to  go  and  pull  my  plug  out,' 
said  Hollo. 


HYDRAULICS.  89 

"  Well,"  said  James ;  and  the  two  boys 
itarted  together  to  go  down  to  the  dam. 

"  Pull  out  the  big  plug,"  said  James. 

"  No,"  said  Hollo  ;  "  the  little  ones  first,  and 
then  the  big  one." 

"  Stop  a  minute,"  said  Miss  Mary. 

The  boys  paused,  and  looked  up  towards 
Miss  Mary.  James  was  standing  upon  the 
bank,  and  Rollo  stood  below  the  dam,  with 
his  hand  upon  one  of  the  plugs. 

"  How  many  little  plugs  are  there  ?  "  she 
asked. 

"  Two,"  said  Rollo. 

"  And  one  is  higher  up  than  the  other." 

"Yes,"  said  Rollo,  "right  over  it;  see;" 
and  he  pointed  to  the  two  plugs,  so  that  Miss 
Mary  could  see  them. 

"Now,"  said  Miss  Mary,  "if  you  pull  out 
the  upper  plug,  the  water  will  not  spout  out 
so  far,  because  it  is  not  pressed  so  hard  by  the 
water  above  it." 

"  Why  not  ?  "  asked  Rollo. 

"  Because,"  said  Miss  Mary,  "  there  is  not  so 
much  water  above  it.  It  is  not  so  far  below 
the  surface.  I  want  you  to  understand 
exactly  the  reason  why  the  water  will  come 
out ;  so  take  a  little  stick  and  run  it  down 
d*  P* 


90  WATER. 

into  the  water,  above  the  dam,  until  you  get 
it  exactly  opposite  to  the  end  of  the  plug." 

Rollo  did  so. 

"  There,"  said  he,  "  I  have  done  it  ex- 
actly." 

"  Well,  now  the  water  that  is  down  as  low 
as  the  end  of  the  stick,  is  pressed  by  all  the 
water  that  is  above  it,  up  to  the  surface,  and, 
as  it  can  move  off  one  way  as  easily  as  an- 
other, wherever  there  is  an  opening,  the  mo- 
ment you  take  out  the  plug,  it  will  at  once 
be  crowded  directly  out  of  the  hole." 

"  Yes,"  said  James,  "  I  understand.  Now, 
Rollo,  pull  it  out." 

"  Well,  out  with  it,"  said  Miss  Mary. 

So  Rollo  pulled  out  the  plug,  and  the 
water  came  spouting  out  after  it,  just  as  they 
had  all  expected.  It  was  projected  a  foot 
or  more  from  the  dam,  and  struck  the 
sand  below,  and  then  ran  off  into  the  ok1 
channel ;  which  had,  however,  now  become 
almost  dry,  on  account  of  the  water  having 
been  stopped  by  the  dam. 

"Now,"  said  Miss  Mary,  "put  in  the  plug 
dgain  a  little." 

Rollo  did  so,  and  then  looked  up  to  Miss 
Mary  to  see  what  he  was  to  do  next. 


HYDRAULICS.  91 

"  Now,"  said  she,  "  put  your  stick  into  the 
Water  as  you  did  before ;  only  this  time  run 
.  it  down  until  it  is  opposite  the  lower  hole." 

Rollo  tried  to  do  so  ;  but  he  could  not  find 
the  end  of  the  lower  plug  very  well,  because 
it  was  concealed  by  the  sand  and  gravel 
which  he  and  James  had  hoed  on.  He, 
however,  pushed  the  sand  away  a  little,  and 
soon  found  it. 

"  It  is  a  good  deal  deeper,  isn't  it  ?  "  asked 
Miss  Mary. 

"Yes,"  said  Rollo,  "half  a  foot." 

"  Then,"  said  Miss  Mary,  "  there  will  be 
half  a  foot  more  of  water  above  it  pressing 
it  down,  and  ready  to  press  it  out,  as  soon  as 
you  take  the  plug  out,  and  give  it  an  opening. 
Of  course  it  will  spout  out  farther.  Pull  it 
out,  and  let  us  see." 

So  Rollo  pulled  out  the  lower  plug,  and 
the  water  spouted  away  a  great  deal  farther 
than  it  had  done  from  the  upper  hole.  Then 
he  asked  Miss  Mary  to  let  him  pull  out  the 
upper  plug  too,  and  let  both  of  them  spout 
together. 

"  And  so  have  two  jets  at  the  same  time," 
said  Miss  Mary. 

"  Yes,"  said  Rollo.     "  Are  they  jets  ?  " 


92  WATER. 

"  Yes,"  replied  Miss  Mary,  "  streams  of 
water  spouting  out  of  a  small  opening  like 
that,  are  called  jets." 

11  Shall  I  pull  it  out  ?  "  said  Hollo. 

"Yes,"  replied  Miss  Mary,  "and  the  liig 
one  too." 

So  Hollo  pulled  them  all  out ;  and  he  and 
James  stood  upon  the  bank  very  much  de- 
lighted to  see  the  three  jets  of  water.  The 
large  hole  was  about  as  low  down  as  the 
lowest  of  the  small  ones,  and  of  course  it 
had  as  much  weight  pressing  down  upon  the 
water  which  came  out  of  it,  and  of  course 
the  water  was  forced  out  just  as  far.  Miss 
Mary  called  upon  the  boys  to  observe  that 
fact. 

"  The  principle  is,"  said  Miss  Mary,  "  that 
the  pressure  is  always  the  same,  at  the  same 
depth,  and " 

"  O  James,"  interrupted  Hollo.  "  see  how 
it  spouts ! " 

"  And  so,  whether  the  hole  is  large  or 
small " 

"  Look  !  look !  "  said  James ;  "  see  what 
a  hole  it  is  digging  into  the  sand !  " 

Miss  Mary  found  that  it  was  vain  to  ex- 
pect them  to  pay  much  attention  to  her  ex- 


HYDRAULICS.  93 

planations  while  such  water-works  were  play- 
ing before  them ;  and  she  might  have  con- 
soled herself  by  reflecting  that  far  more  dis- 
tinguished lecturers  than  herself  often  find 
their  experiments  more  attractive  than  their 
theories. 

She  did  not,  therefore,  attempt  to  philoso- 
phize any  more,  but  went  down  close  to  the 
bank,  where  she  could  see  more  distinctly, 
and  watched  the  water  from  the  jets  as  it 
plunged  into  a  sort  of  basin,  which  it  soon 
formed  in  the  sand  below,  and  then  ran  off, 
happy  in  its  release,  to  fill  the  channels  which 
had  become,  by  the  stoppage  of  the  water 
above,  nothing  but  a  succession  of  little  stag- 
nant pools. 

At  last  she  said  that  it  was  time  for  her  to 
go  home,  and  Hollo  and  James  concluded 
that  they  would  go  too.  So  they  walked 
along  towards  home  together.  Before  they 
left  the  dam,  however,  they  put  the  three 
plugs  in  again  safely,  because,  as  Hollo  said, 
he  wanted  to  have  the  dam  brimming  full 
when  he  should  come  down  to  see  it  the 
next  morning. 


94  WATER. 


QUESTIONS. 

What  was  Miss  Mary's  definition  of  a  fluid  ?  Is  brass  a 
fluid?  Is  sponge?  Did  either  of  the  boys  think  that 
sponge  was  a  fluid?  Why,  probably,  did  he  think  sof 
What  is  a  semi-fluid  ?  What  examples  did  Miss  Mary 
give  of  a  semi-fluid  ?  What  example  did  Miss  Mary  give 
to  illustrate  the  meaning  of  the  \vordpropcrty?  Did  Rollo 
at  first  remember  the  explanation  which  his  father  had 
given  him  before  of  this  word  ?  What  was  the  second 
property  of  water  which  Miss  Mary  mentioned  ?  What 
led  her  to  think  of  it '  Did  Miss  Mary  expect  that  the 
water  would  spout  out  more  forcibly  from  one  of  the  holes 
than  from  another  ?  Whica  one  ?  Why  ?  What  name 
did  she  give  to  the  streams  of  water  spouting  out  from  the 
boles  in  the  board  ? 


CHAPTER    VII. 

THE   MEASURE  OF  PRESSURE. 

WHEN  Rollo  got  home,  he  found  that  his 
father  had  not  yet  come,  and  that  supper  was 
not  quite  ready ;  and  so  he  thought  he  would 
go  and  meet  his  father.  He  accordingly  took 
his  hoop,  and  ran  out  of  the  gate  into  the 
road,  hoping  that  he  might  overtake  James, 
who,  he  supposed,  could  not  have  gone 
very  far. 

He  did  not  overtake  him,  for  James  had 
left  the  main  road  to  go  home  by  a  cross 
path,  through  the  woods  and  fields.  So 
Rollo  went  on  alone,  trundling  his  hoop,  un- 
til he  came  to  a  bridge  which  led  over  a 
brook,  which  the  road  had  to  cross.  He 
stopped  here,  and  leaned  over  the  railing  of 
the  bridge,  to  look  down  into  the  water. 

It  was  a  large  brook,  and  there  was  a  mill 
upon  it,  at  a  little  distance  below.  There 
was  a  dam  at  the  mill.  There  is  always  a 


96  WATER. 

flam  where  there  is  a  mill  upon  a  stream  of 
water,  to  keep  back  the  water,  and  make  it 
rise  high  in  the  pond  above  the  dam.  The 
pond  above  this  mill-dam  extended  back 
nearly  to  the  bridge,  so  that  the  water  under 
the  bridge  was  not  a  rapid  stream,  tumbling 
and  foaming  along ;  but  it  was  deep  and 
almost  still. 

"Now,"  said  Hollo  to  himself,  "I  can  tell 
whether  the  water  is  level.  I'll  throw  a 
stick  in." 

His  idea  was,  that,  if  the  water  was  level, 
there  would  be  no  current ;  but  that,  if  there 
was  any  current,  so  as  to  float  the  stick  slowly 
down  under  the  bridge,  then  there  would  be 
a  current  made  by  the  water's  seeking  its 
level. 

So  he  threw  in  a  little  stick.  At  first,  it 
floated  a  little  way  up  the  stream,  being 
driven  by  the  impulse  which  he  had  given 
it,  in  throwing  it.  But  it  moved  more  and 
more  slowly,  as  its  momentum  —  that  is,  the 
force  with  which  it  was  moving  —  was  gradu- 
ally extinguished  by  the  resistance  of  the 
water,  and  then  it  began  slowly  to  move  the 
other  way.  Hollo  observed  also  several  little 


'WHAT  ARE  YOU  SPECULATING  UPON  NOW?"— Pago  97. 


THE    MEASURE    OF    PRESStTRE.  97 

bubbles,  and  one  or  two  dried  leaves,  all 
coming  down  in  the  same  direction  to- 
wards the  bridge. 

"Yes,"  said  he,  "  there  is  a  current." 

Just  at  that  moment  his  father  came  along. 
Rollo  did  not  observe  him  until  he  had  got 
very  near  him. 

"  Well,  Rollo,"  said  his  father,  "  and  what 
are  you  speculating  upon  now  ?  " 

"Why,  father,"  said  Rollo,  "you  see  this 
water? " 

"  Yes,"  said  his  father. 

"  Well,  does  not  it  look  as  if  the  surface  of 
it  was  level  ?  " 

"  Yes,  it  does  appear  sensibly  level." 

"  What  do  you  mean  by  sensibly  level  ?  '•' 
said  Rollo.  "  I  don't  see  that  water  can  be 
sensible  at  all." 

"  I  did  not  say  it  was  sensible,"  rejoined 
his  father,  "but  sensibly  level,  —  which 
means  level  so  far  as  can  be  perceived  by 
the  senses,  that  is,  by  seeing  or  feeling.  This 
water  is  sensibly  level ;  that  is,  I  do  stot  see 
that  one  part  is  any  higher  than  another,  and 
yet  we  know  that  moving  water  never  can 
be  level ;  for  the  difference  of  level  is  all  that 
makes  it  move." 

6  9 


g»3  WATER. 

"  Well,  father,  is  not  a  pond  level  ?  "  said 
Rollo. 

"No,"  said  his  father,  "not  generally." 

u  O  father !  "  said  Rollo,  with  surprise ; 
"  I  thought  that  still  water  was  always  per- 
fectly level." 

"  What  made  you  think  so  ?  " 

"Miss  Mary  told  us  so." 

"  Very  well ;  she  was  correct.  But  sup- 
pose I  had  said  that  a  pond  was  level, — 
what  then?" 

"  Why,  I  was  going  to  say,"  replied  Rollo, 
"that  there  might  be  a  little  brook  come 
into  it  at  one  end,  and  run  through  it,  and 
out  at  the  other  end ;  and  so  the  water  might 
move  along  through  the  pond,  while  yet  it 
was  level." 

"  No,"  said  his  father ;  "  for  it  is  only  still 
ponds  that  are  level,  not  ponds  which  have 
brooks  running  through  them.  Because, 
\f  a  brook  were  to  run  in  at  one  end,  the  wa- 
ter would  accumulate  and  rise  at  that  end, 
and  so  that  end  would  become  the  highest, 
Then  the  water  at  that  end,  being  raised  a 
little  higher  than  at  the  other,  though  not 
sensibly  higher,  would  press  and  settle  away 
towards  the  other  end ;  but,  as  fast  as  it  settled 


THE    MEASURE    OF    PRESSURE.  9 

away,  more  would  come  in  from  the  brook; 
and  as  fast  as  it  moved  towards  the  other 
end,  it  would  flow  out  through  the  outlet." 

"Yes,  father,"  said  Rollo,  "I  see." 

"  And  so  it  is  with  ponds  as  with  all  othei 
water  ;  where  there  is  a  current,  we  may  be 
sure  that  the  surface  is  not  level." 

"So  that  I  could  skate  easier  one  way  than 
the  other,"  said  Rollo. 

"  There  would  not  be  any  sensible  differ- 
ence," said  his  father. 

While  they  had  been  holding  this  conver- 
sation, Rollo  and  his  father  had  been  walking 
along  slowly;  and  now  they  had  reached 
home.  Rollo 's  father  told  him  that  he 
would  tell  him  something  more  about  the 
subject  after  supper. 

Accordingly,  after  supper,  when  Mr.  Holi- 
day had  taken  his  seat  by  a  window  which 
opened  towards  the  setting  sun,  Rollo  came 
and  asked  him  to  tell  him  then.  Rollo  took 
his  seat  in  a  little  rocking-chair  by  his  fa- 
ther's side. 

"]n  speaking  of  the  pressure  of  water," 
said  his  father,  "  there  is  one  word  which  is 
used  a  great  deal,  and  which  it  is  important 
that  you  should  understand." 


100  WA1ER. 

"Well,  sir,"  said  Hollo,  "and  what  wo-d 
is  it?" 

"  Column"  answered  his  father. 

"Column?"  said  Hollo.  "I  believe  1 
know  what  column  means." 

"  What  does  it  mean  ?  "  said  his  father. 

"Why,  —  it  means, — I  can't  tell  exactly; 
but  it  is  something  about  a  building." 

"  Yes,  a  tall  pillar,  in  building,  is  called  a 
column.  A  column  of  water  is  much  the 
same  in  form.  Suppose  there  were  a  dollar 
lying  flat  upon  the  bottom  of  a  tub  of  water. 
Now,  all  the  water  which  would  be  exactly 
above  this  dollar,  from  the  dollar  itself  up  to 
the  surface  of  the  water,  would  be  called  a 
column.  You  see  it  would  be  of  the  form 
of  a  column  or  pillar  in  building." 

"  Yes,  sir,"  said  Rollo. 

"  Now,  if  there  were  a  hole  in  the  bottom 
of  the  tub,  just  of  the  size  of  the  dollar,  and 
the  dollar  were  to  be  fitted  into  it  exactly, 
and  then  the  tub  filled  with  water,  the  dollar 
would  have  resting  upon  it  only  the  weight 
of  that  column  of  water  which  was  exactly 
over  it." 

"  Yes,  sir,"  said  Rollo. 

"Because,  you    see,"    added    Ids    father, 


THE    MEASURE    OK    PRESSURE .  101 

"  that  the  rest  of  the  water  would  rest  upon 
the  other  parts  of  the  bottom  of  the  tub.  By 
this  plan  you  can  calculate  how  great  the 
pressure  will  be  upon  any  part  of  the  bottom 
of  a  tub,  for  it  will  always  be  just  as  great  as 
the  weight  of  a  column  of  water  as  large  as 
the  part,  and  as  high  as  up  to  the  surface  of 
the  water. 

"And  it  is  just  so,"  continued  his  father, 
"upon  the  side,  because  water  presses  side- 
ways just  as  much  as  it  does  downwards." 

"  Yes,  sir,"  said  Hollo ;  "  Miss  Mary  ex- 
plained that  to  us.  She  said  it  was  because 
the  water  moved  so  easily." 

"Yes,"  added  his  father;  "the  particles 
move  easily  among  themselves,  and  so  trans- 
mit motion  and  pressure  in  every  direction." 

Rollo  did  not  understand  exactly  what  his 
father  meant  by  transmitting  motion  and 
pressure  ;  but  he  did  not  ask  for  an  explana- 
tion, and  so  his  father  went  on. 

"  Therefore,  if  the  hole  which  the  dollar  is 
made  to  fit  into,  is  in  the  side,  the  pressure 
of  the  water  upon  it  would  be  exactly  the 
same  with  the  pressure  upon  it  when  it  is 
on  the  bottom,  were  it  not  for  one  circum- 
stance." 

9* 


102  WATER. 

"  What  is  that  ?  "  said  Rollo. 

"  Why,  the  hole  being  upon  the  side,  is 
cannot  be  down  so  low  as  if  it  were  upon 
the  bottom.  Only  the  lower  edge  could  be 
as  low  as  the  bottom,  and  just  along  this 
lower  edge  the  water  would  press  as  hard 
upon  the  opening  in  the  side,  as  it  would 
upon  an  opening  in  the  bottom.  But  the 
upper  part  of  the  hole  would  be  nearer  the 
surface,  and  of  course  would  not  be  pressed 
so  hard. 

"  Therefore,"  continued  Hollo's  father,  "  it 
we  wish  to  know  how  great  the  pressure  of 
the  water  would  be  upon  any  space  in  the 
side  of  the  vessel,  we  must  take  the  middle 
of  the  space  as  the  average  depth  from  the 
surface,  and  then  the  pressure  upon  it  will  be 
as  great  as  the  weight  of  a  column  of  watei 
as  large  round  as  the  space  is,  and  as  high 
'as  it  is  from  the  centre  of  the  space  to  the 
surface  of  the  water.  Do  you  understand 
this?" 

"  Why,  — pretty  well,"  said  Rollo. 

"Not  perfectly  well  ?  "  inquired  his  father, 

"  Why,  not  quite  so  well  as  what  Miss  Mary 
explained  to  us." 

His  father  laughed,  and  said,  "  I  suppose  I 


THE    MEASURE    OF    PRESSURE.  103 

am  not  quite  so  good  a  lecturer  as  Miss  Mai  y 
is.  But  when  did  she  tell  you  anything 
about  this? " 

"  This  afternoon,"  answered  Rollo,  "down 
by  our  dam." 

"  Your  dam  ?  "  said  his  father.  "  I  did  not 
laiow  that  you  had  any  dam." 

"  Yes,  sir,"  said  Rollo ;  and  he  explained 
to  nis  father  how  they  had  made  a  dam, 
under  Jonas's  directions,  and  how  Miss  Mary 
had  made  use  of  it  as  a  piece  of  apparatus, 
illustrative  of  the  doctrines  of  hydraulics. 

"  And  there !  "  continued  Rollo,  "  I  prom- 
ised to  go  and  tell  Jonas  how  our  dam  suc- 
ceeded ;  and  I  must  go  now." 

"  Wait  a  minute,"  said  his  father ;  "  let  me 
first  question  you  a  little  upon  what  I  have 
been  explaining  to  you.  Suppose  that  a  tub 
of  water  were  to  be  suspended  in  such  a  way 
that  you  could  get  at  the  bottom  of  it,  and  a 
hole  were  made  in  the  bottom  as  large  as  you 
could  cover  with  the  palm  of  your  hand  ; 
now,  if  you  were  to  put  your  hand  there,  and 
attempt  to  keep  the  water  from  coming  out, 
how  much  weight  should  you  have  to 
support  ? " 

"  I  don't  know,  sir,"  said  Rollo. 


104  WATER. 

"  I  do  not  mean  how  much  the  weight 
would  be  in  pounds,  but  how  big  a  column 
would  it  be  ?  " 

"0,  as  big  as  my  hand,"  replied  Hollo. 

"  Yes,  as  big  round  as  your  hand  at  the 
bottom." 

"  Yes,  sir,"  said  Hollo,  "  and  as  high  as  up 
to  the  top  of  the  tub." 

"  But  suppose  the  tub  was  not  quite  full." 

"  O,  then,"  replied  Hollo,  "  only  as  high 
as  to  the  top  of  the  water." 

"  Suppose  the  hole  was  in  the  side  of  the 
tub,  instead  of  in  the  bottom  ?  " 

"  Then  it  would  be  just  the  same,"  said 
Hollo. 

"  That  is,"  continued  his  father,  "  the  pres- 
sure would  be  equal  to  the  weight  of  a 
column  as  large  round  as  your  hand,  and  as 
high  as  from  the  surface  of  the  water  down 
to  —  what?" 

"  Why,  down  to  the  hole,"  said  Hollo. 

"  Which  part  of  the  hole  ?  "  asked  1'is  fa- 
ther ;  "to  the  top,  or  the  bottom ?  " 

"0,  to  the  middle,"  said  Hollo;  '  that 
would  be  the  average." 

"Well,"  said  his  father,  "do  you  think 
jrou  could  hold  your  hand  so,  covering  such 


THE    MEASURE    OF    PRESSURE.  105 

a  hole  in  the  side  of  a  tub  full  of  water,  and 
keep  it  in  ?  " 

"Yes,  sir,"  said  Rollo,.  "easily  enough." 

"  Hold  out  your  hand  a  minute,"  said  his 
father. 

Rollo  held  out  his  hand,  as  his  father  had 
requested. 

"  Now,"  said  he,  '•'  put  the  other  hand  up 
over  it  about  as  high  as  from  the  bottom  to 
the  top  of  a  tub." 

Rollo  did  so,  and  said,  — 

"  There,  I  should  think  that  the  top  of  the 
tub  would  come  about  here." 

"  Well,  now,  should  you  be  strong  enough 
to  hold  up  in  your  hand  a  piece  of  ice  as 
large  round  as  the  palm,  and  as  high  as  that  ?  " 

"  Yes,  sir,"  said  Rollo,  "  only  it  would  be 
very  cold." 

"  Never  mind  that ;  I  only  suppose  it  to  be 
ice,  because  you  can  more  easily  imagine  ice 
in  *he  form  of  such  a  column  than  water; 
though  ice  would  be  lighter,  and  so  it 
would  take  a  longer  column.  Now,  consider 
how  hard  a  pressure  you  would  have  to  resist 
to  stop  such  a  hole  near  the  bottom  of  a  hogs- 
head, if  it  was  full  of  water." 

"  Why,  then  "  said  Rollo,  "  I  should  have 


106  WATER. 

to  hold  hard  enough  to  hold  up  a  column  as 
long  as  the  hogshead." 

"  And  could  you  do  that  ?  " 

"No,  sir,"  said  Hollo,  "I  don't  think  1 
could." 

"  Ii  you  were  to  try,  by  putting  your  haiul 
over  the  hole  when  the  hogshead  was  empty, 
and  then  letting  them  fill  it  up  gradually,  at 
last  you  would  find  it  impossible  to  resist  the 
pressure,  but  the  water  would  spirt  out  be- 
tween your  hand  and  the  hole  in  all  direc- 
tions." 

"  I  wish  I  could  try  it,"  said  Hollo. 

"  I  don't  see  but  that  you  understand  what 
I  explained  to  you  pretty  well,"  said  his  fa- 
ther. "  You  see  what  the  calculation  de- 
pends upon,  so  that  I  am  not  so  much  inferior 
to  Miss  Mary  as  a  lecturer,  after  all.  Well, 
now  you  may  go  and  tell  Jonas  about  your 
dam." 

So  Rollo  left  his  father,  and  ran  off  to 
look  for  Jonas.  He  found  him  in  the  barn, 
pitching  down  some  hay  for  the  horses. 

'•  Well,  Jonas,"  said  Rollo,  as  he  climbed 
up  the  ladder,  to  the  scaffold  where  Jonas 
&*as  standing. 

"  Well,  Rollo,"  answered  Jonas. 


THE    MEASURE    OF    PRESSURE.  10? 

"  I've  come  to  tell  you  about  our  dam." 

"  Yes,"  said  Jonas,  "  1  see  you  have  got  a 
fine  head  of  water  in  it." 

"  Head  of  water  ?  "  repeated  Rollo,  inter- 
rogatively. He  did  not  know  exactly  what 
Jonas  meant. 

"  Yes,"  said  Jonas,  "  head  of  water.  The 
perpendicular  height  of  water  raised  by  a 
dam,  they  call  the  head.  I  should  think 
that  you  had  eight  or  ten  inches  head.': 

"  Father  calls  it  column"  said  Rollo. 

"  Column  ? "  repeated  Jonas,  interrogative- 
ly, in  his  turn. 

"Yes,"  said  Rollo,  "column." 

Rollo  was  not  quite  right  in  this ;  for  his 
father  had  not  used  the  word  column  in  the 
same  sense  and  connection  in  which  Jonas 
used  his  phrase.  However,  he  forgot  this 
apparent  disagreement  immediately,  for  Jonas 
told  him  that  he  ought  not  to  have  left  the 
plugs  in,  when  he  came  away  from  the  dam. 

"  Why  not  ?  "  said  Rollo. 

"Because,"  said  Jonas,  "if  you  had  taken 
out  the  plugs,  the  water  would  have  been  let 
off  through  the  holes,  and  would  not  have 
risen  so  high." 

"  But  we  want  it  to  rise  high,"  said  Rolla 


108  WATER. 

"  Not  when  you  are  at  home,  and  in  bed 
and  asleep,"  said  Jonas. 

<  Will  it  do  any  harm  ?  "  said  Hollo. 

"  It  puts  your  dam  in  danger,"  said  Jonas. 

"  How  ?  "  said  Hollo. 

"Why,  in  two  ways,"  said  Jonas.  "In 
the  first  place,  the  higher  it  rises,  the  greater 
the  pressure  will  be  about  the  under  edge  of 
the  board,  and  the  greater  the  danger  is  that 
the  dam  will  blow." 

"  Blow  ?  "  said  Rollo ;  "  what  do  you  mean 
by  blow  ? — leak  ?  If  it  does  leak  a  little,  we 
can  stop  it  again  by  hoeing  on  more  sand 
and  gravel." 

"  You'll  find,  I  rather  think,"  said  Jonas, 
"  that  your  hoeing  on  sand  and  gravel  will 
not  do  much  good,  in  stopping  a  hole,  when 
you  have  ten  inches'  head  of  water  on." 

Rollo  did  not  understand  all  this  very  well, 


would  be. 

"  Why,  the  water,  now,  has  no  way  of 
escape  but  over  the  top  of  the  board ;  for  it 
must  continue  to  run  in  until  it  fills  the  dam 
full,  and  then  the  surplus  will  run  over  the  top. 
Now,  the  water  which  runs  over  will  fall 
down  close  to, the  under  side  of  the  board 


THE    MEASURE    OF    PRESSURE.  09 

and  will  gradual  .y  dig  out  a  hole  there  ;  aud 
it  may  before  to-morrow  morning  underm  JIG 
the  dam,  and  let  the  water  through." 

"  Then,"  said  Rollo,  "  I  wish  I  had  taken 
out  the  plugs." 

"  Yes,"  said  Jonas,  "  that  would  have  been 
safer.  However,  there  is  one  advantage  in 
leaving  them  in,  and  letting  the  water  run 
over." 

"  What  is  that  ?  "  said  Rollo. 

"  Why,  all  the  dirt  and  leaves,  &c.,  will 
be  drawn  off  from  the  surface  of  the  water, 
and  will  run  over  the  dam,  so  that,  if  the  dam 
stands  safe  until  morning,  the  water  will  be 
clear  and  beautiful." 

"Then,"  said  Rollo,  "I'll  let  it  stay  as 
it  is." 

"  And  take  the  risk  ?  "  said  Jonas. 

"  Yes,"  said  Rollo  ;  "  Miss  Mary  will  like  to 
see  it  look  clear  and  beautiful." 

"  Is  she  coming  to  give  you  another 
lecture  ?  "  said  Jonas. 

"Yes,"  said  Rollo,  "I  hope  she  will." 

u  Well,"  said  Jonas,  "  and  to-morrow  even- 
ing ril  come,  and  give  you  a  lecture." 

"  O  Jonas,"  said   Rollo,  laughing,   "  you 
cannot  give  a  lecture." 
10 


1  1  0  WATER. 

"  Why  not  ? "  said  Jonas. 

"  O,  because,"  said  Hollo,  "  Miss  Mary  is 
a  teacher." 

"  So  am  I,"  said  Jonas ;  "  at  any  rate,  if 
you  will  get  James  to  come  and  help  you 
make  an  audience,  you  may  see  if  I  can't 
lecture." 

11  Well,"  said  Hollo,  "  we  will." 


QU  E  S  T  IO  N  S. 

What  was  Hollo  thinking  of  when  he  was  looking  over 
the  bridge  ?  How  was  he  going  to  ascertain  whether  the 
surface  of  the  water  was  level  ?  Did  he  find  that  there 
•was  any  current  ?  Is  a  pond  generally  perfectly  level  ? 
'How  did  Hollo's  father  show  that  a  pond  would  generally 
ihave  a  descent  ?  What  is  a  column  ?  How  is  the  pressure 
of  water  upon  any  part  of  the  bottom  of  a  vessel  measured  ? 
How  is  the  calculation  made  when  the  part  is  upon  the 
•side  of  the  vessel?  What  peculiar  expression  did  Jonas 
use  when  he  was  speaking  of  Hollo's  dam?  What  did  he 
mean  by  it'  Did  he  think  that  the  dam  was  perfectly 
*afe  ?  What  two  dangers  did  he  think  it  exposed  to  ? 


CHAPTER    VIII 

BLOWING. 

ROLLO  had  another  lecture  from  Miss  Mary 
before  he  had  an  opportunity  to  listen  to 
Jonas's  performance.  The  appointment  for 
this  second  lecture  of  Miss  Mary's  was  made 
in  a  somewhat  singular  way,  as  follows  :  — 

The  morning  after  the  conversation  with 
Jonas  on  the  scaffold  in  the  barn,  Rollo  rose 
early  to  go  down  before  breakfast,  and  see  if 
his  dam  had  been  carried  away.  To  his 
great  joy,  he  found  it  all  safe.  The  water, 
too,  was  beautifully  clear  and  transparent, 
and  it  extended,  in  a  smooth  and  glassy  sheet, 
for  a  considerable  distance,  up  between  the 
banks  of  the  brook.  A  thin  sheet  of  watqr 
was  gliding  over  the  edge  of  the  board,  and 
falling  down  into  a  little  basin,  which  it  had 
itself  made  in  the  sand  below.  Thence  it 
meandered  off,  down  the  bed  of  the  brook 
and,  as  far  down  as  Rollo  could  see,  the  little 


i  12  WATER. 

bticam  appeared  to  flow  quietly  along,  just 
as  i  f  no  dam  had  been  built. 

J.ist  at  this  moment,  Hollo's  eye  caught 
s:>mrtthiRg  white  upon  the  top  of  one  of  the 
stakes  which  Jonas  had  driven  down  behind 
the  board  to  support  it  in  its  place.  It  was  a 
piece  of  paper  folded  once.  A  small  stone 
from  the  brook  was  laid  upon  it,  to  keep  it 
from  being  blown  away.  Hollo  took  the 
stone  off,  and  found  his  own  name  written 
upon  he  back  of  the  paper.  He  opened  it, 
and  n  i  as  follows  :  — 

"  DEAI    ROLLO, 

In  taking  my  morning  walk,  I  came 
down  to  ;ee  your  dam.  How  beautiful  and 
clear  the  water  looks !  I  shall  take  a  walk 
again  thL.  afternoon  at  five  o'clock,  and,  if 
you  and  J.«mes  will  be  here,  I  will  come  and 
give  you  another  lecture. 

Miss  MARY." 

Rollo  was  very  much  pleased  to  receive 
this  note. 

"  I  wish,"  said  he  to  himself,  "  that  I  had 
known  that  Miss  Mary  was  coming  here  so 


BLOWING.  113 

early ;  for  then  I  would  have  come  down 
too,  and  so  I  should  have  been  here  with 
her.  No,  I  don't,  either,"  said  he  ;  "  for  then 
I  should  not  have  had  this  note." 

Rollo  showed  the  note  to  his  mother  at 
breakfast,  and  she  gave  him  leave  to  go  after 
dinner  and  ask  James  to  come  and  play  with 
him  that  afternoon,  so  as  to  be  ready  to  hear 
Miss  Mary's  lecture  at  five  o'clock.  It  was 
about  three  o'clock  when  James  came,  and 
they  found  all  safe  at  the  dam. 

Rollo  soon  proposed  that  they  should  pull 
out  the  plugs,  and  let  the  water  run  out  of 
the  holes,  instead  of  running  over  the  board ; 
for,  as  he  told  James,  Jonas  said  that  that 
would  be  safer. 

"  It  would  be  a  pity,"  said  he,  "  to  have 
our  dam  carried  away  now,  before  Miss  Mary 
comes." 

"Well,"  said  James,  "let  us  pull  them 

OJt" 

So  the  boys  pulled  out  the  great  plug,  I  tit 
they  could  not  get  the  small  ones  out.  In 
fact,  the  great  one,  which  they  did  pull  out, 
came  very  hard.  Rollo  said  he  wondered 
what  made  it  come  so  hard.  The  reason 
was,  that  it  had  swelled,  and  so  had  become 
e*  10* 


114  WATER. 

very  tight  in  the  hole.  Wood  always  swells 
when  it  is  soaked  with  water.  This  property 
of  water  to  swell  wood,  by  insinuating  itself 
into  its  pores,  was  a  property  which  Hollo 
was  not  acquainted  with  ;  or,  if  he  had  heard 
of  it  before,  he  did  riot  think  of  it  now,  in 
application  to  this  case. 

"Do  you  think,  James,"  said  Hollo,  "that 
the  water  will  run  out  through  this  hole  as 
fast  as  it  comes  down  the  brook,  so  that  it 
will  not  run  over  the  top  of  the  board  ?  " 

"  I  don't  know,"  said  James. 

"  We  shall  soon  see,"  said  Rollo  ;  "  let  us 
go  and  sit  down  upon  the  bank,  and  watch  it." 

So  they  went,  and  sat  down  upon  the  bank, 
and  watched  the  water,  as  it  spouted  out  of 
the  hole.  The  water  very  soon  ceased  to 
run  over  the  top  of  the  board.  This  was  in 
such  a  dry  season  of  the  year,  that  very  little 
water  was  flowing  in  the  brook ;  so  little, 
that  it  could  flow  out  through  the  hole  a 
little  faster  than  it  came  in  from  the  brook 
above.  Of  course  the  surface  of  the  water 
111  the  pond,  formed  by  the  dam,  began  to 
subside,  and,  after  a  few  minutes,  it  had  set- 
tled as  much  as  an  inch  below  the  edge  of 
the  board. 


BLOWING.  115 

"  We  shall  Jose  all  our  pond,"  said  James 

"No,"  said  Rollo,  "it  will  only  settle 
down  as  far  as  the  hole,  and  that  will  leave 
considerable  water  in  the  dam.  And  then, 
besides,"  continued  Rollo,  "when  it  has  all 
run  out,  down  to  the  hole,  we  can  put  the 
plug  in,  and  let  it  fill  up  again." 

They  watched  the  water  for  some  time, 
but  they  found  that  prejty  soon  it  did  not 
spout  out  as  far  as  it  did  at  first.  The  jet 
seemed  to  be  less  and  less  powerful,  as  the 
water  settled  gradually  on  the  inside ;  be- 
cause, as  Rollo's  father  would  have  expressed 
it,  the  column  of  water  that  produced  the 
pressure  which  forced  the  water  out  through 
the  hole,  was  gradually  diminishing  in  height ; 
or,  as  Jonas  would  have  stated  it,  there  was 
less  head  of  water  in  the  dam,  to  force  the 
water  through. 

The  boys  waited  for  some  time,  expecting 
that  the  surface  of  the  water  would  subside 
to  the  level  of  the  hole  ;  but  it  did  not ;  it 
settled  slowly  down,  until  it  was  only  about 
two  inches  above  the  hole,  and  there  it 
seemed  to  stop.  After  watching  it  for  some 
time,  they  did  not  perceive  that  it  was  set- 
tling any  farther.  They  wondered  why  it  did 


116  WATER. 

not  continue  to  subside  until  it  reached  the 
level  of  the  hole  where  it  was  running  out. 

"  Why,  the  reason  is,"  said  James,  "  that 
the  hole  is  not  big  enough." 

•'<  Why,  it  is  a  pretty  big  hole,"  said  Rollo. 

"  Yes,"  replied  James,  "  but  it  is  not  big 
enough  to  let  the  water  through  so  fast  as  it 
comes  into  the  dam  down  the  brook." 

"  Why,  yes  it  is,  James,"  replied  Rollo ; 
"  for,  when  we  first  pulled  out  the  plug,  it  let 
the  water  run  out  faster  than  it  ran  in,  and 
lowered  the  water  in  the  dam.  I  don't  see 
why  it  don't  keep  on  lowering  it." 

James  could  not  remove  this  difficulty, 
and  so  Rollo  put  the  plug  in  again,  and  let 
the  dam  fill  up.  Then  he  pulled  out  the 
plug,  and  saw  that  the  water  settled  quite 
fast  for  a  time,  until  the  surface  had  subsided 
about  to  the  same  level  as  before ;  but  it  did 
not  go  down  as  low  as  to  the  top  of  the  hole. 

He  could  not  explain  this  remarkable 
operation  at  all,  and  they  determined  to  ask 
Miss  Mary  to  explain  it  in  her  lecture. 

Miss  Mary  came  about  five  o'clock,  and 
the  boys  immediately  asked  her  to  explain 
why  the  water  did  not  all  run  out  through 
the  hole,  since  a  part  of  it  could  run  out  sc 


BLOWING.  117 

easily.  They  then,  in  order  to  show  Miss 
Mary  that  the  difficulty  was  a  real  one,  put 
the  plug  in,  and  let  the  dam  fill  up.  Then 
they  pulled  it  out,  and  very  soon  the  water 
began  to  settle. 

"  There,"  said  James,  "  you  see  the  hole 
is  big  enough  to  let  out  all  the  Tjrater  that 
runs  in  the  brook ;  for  .°ee !  "  he  continued, 
pointing  to  the  little  stream  which  was  run- 
ing  in  all  the  time,  at  the  head  of  the  pond, 
"  see !  the  water  keeps  running  in,  and  it 
must  run  out  faster  through  the  hole,  or  else 
it  would  not  go  down." 

"  Yes,"  said  Miss  Mary ;  "  it  certainly 
runs  out  faster  now  that  the  whole  pressure 
is  on." 

"  What  whole  pressure  ?  "  asked  Hollo. 

"  Why,  the  whole  pressure  of  the  water. 
For  the  dam  was  full  when  you  took  the  plug 
out,  and  so  the  hole  was  about  six  inches 
below  the  surface  of  the  water;  and  thus 
there  was  the  pressure  of  a  column  of  six 
inches,  to  force  the  water  out ;  and  you  see 
it  spouts  out  with  considerable  force.  But  by 
and  by,  if  the  water  should  subside  until  it  is 
down  within  two  inches  of  the  hole,  then 
there  would  only  be  a  column  of  two  inches 


118  WATER. 

pressing ;  and,  accordingly,  it  would  spout 
out  with  only  one  third  the  force.  This, 
very  likely,  would  not  carry  it  off  as  fast  as  it 
comes  in.  So,  in  fact,  the  water  will  subside 
until  the  height  of  the  column  is  just  enough 
to  force  the  water  out  as  fast  as  it  fills  up, 
from  the  brook  above,  and  then  the  surface 
will  remain  stationary." 

In  order  to  make  this  plain,  Miss  Mary 
asked  the  boys  to  pull  out  all  three  of  the 
plugs,  and  she  would  try  the  experiment  in 
another  form. 

"  They  won't  come  out,"  said  Hollo. 

"  Why  not  ? "  said  Miss  Mary. 

"I  don't  know,"  said  Hollo,  "only  they 
won't  come  out." 

"  I  wish  that  I  could  get  down  to  them," 
said  Miss  Mary ;  "  I  rather  think  I  could  get 
them  out." 

After  some  hesitation,  she  at  length  stepped 
cautiously  down  upon  the  pieces  of  wood 
which  the  boys  had  placed  below  the  dam, 
and  very  carefully  pulled  out  the  small  plugs. 
They  were  in  very  tight ;  even  Miss  Mary 
found  it  very  hard  to  draw  them  out. 

"  There,"  said  she,  "  now  perhaps  the  wa- 
ter will  all  run  out,  as  low  as  the  lowest  hole.'; 


BLOWING. 

Miss  Mary  was  right.  The  Water  did 
settle  down  very  low,  nearly  or  quite  down 
to  the  top  of  the  large  hole. 

"  Now,"  said  she,  "  we  will  put  in  the  two 
small  plugs,  and  leave  the  large  one  out,  and 
we  shall  see  what  the  effect  will  be." 

So  the  boys  went  and  sat  down  with  Miss 
Mary  upon  the  bank,  and  watched  the  effect. 

"You  see,"  said  Miss  Mary,  "that  the 
water  is  gradually  rising.  The  great  hole  is 
not  large  enough  to  let  the  water  pass 
through  as  fast  as  it  comes  in  above,  unless 
there  is  some  pressure  upon  it.  The  water 
is  rising." 

"Yes,"  said  James,  "I  can  see  a  little 
stick  by  the  shore,  which  is  almost  covered ; 
there,  the  water  is  over  it." 

"  But,  as  the  Avater  rises,"  said  Miss  Mary, 
"  you  see  it  presses  harder  and  harder  through 
the  hole,  and  the  jet  spouts  out  farther  and 
farther." 

"Yes,"  said  Hollo,  "I  see  it  does." 

"  Now,"  continued  Miss  Mary,  "  after  a 
time,  the  water  will  rise  so  high  as  to  produce 
a  pressure  great  enough  to  force  the  water 
through  as  fast  as  it  comes  down  from  above, 
Then  the  coming  in  of  the  water  from  above, 


120  WATER. 

and  its  escape  through  the  hole,  will  be  just 
equal,  and  the  water  will  neither  rise  nor  fall. 
The  effect  of  the  supply  coming  in  from 
above,  tending  to  raise  the  water,  and  that 
of  the  escape  from  the  hole,  tending  to  lower 
it,  will  be  in  equilibrium." 

"Equilibrium!  "  said  Rollo;  "what  does 
that  mean  ? " 

"  It  means  that  they  will  be  exactly  equal, 
so  as  to  balance  each  other,"  replied  Miss 
Mary. 

"Now,"  continued  Miss  Mary,  "if  the 
hole  were  smaller,  the  water  would  have  to 
rise  to  a  higher  level  before  the  pressure 
would  be  sufficient  to  carry  out  the  water  as 
fast  as  it  comes  in." 

"  Let  us  try  it,"  said  Rollo. 

"  Well,"  said  Miss  Mary,  "  we  can  try  it 
by  means  of  one  of  the  small  plugs." 

So  Rollo  went  down  to  the  dam,  and  took 
out  the  lower  small  plug,  and  put  in  the  large 
one.  The  lower  small  plug  was  just  at  the 
level  of  the  large  one,  and  of  course  the  wa- 
ter passing  out  of  it  was  subject  to  the  same 
pressure.  And  though  the  jet  was  smaller, 
because  the  hole  was  smaller,  yet  it  spouted 
out  to  about  the  same  distance. 


BLOWING.  121 

Hollo  came  back  to  the  bank,  and  they 
found  that  tbe  water  gradually  rose  until  it 
nearly  reached  the  top  of  the  board,  and  still 
continued  rising. 

"  I  don't  believe  but  that  it  will  run  over," 
said  Hollo. 

"Very  likely,"  said  Miss  Mary;  "you  see 
that  that  hole  is  a  great  deal  smaller  than  the 
other,  and  of  course  it  will  take  a  great  pres- 
sure to  force  the  water  through  as  fast  as  it 
Tomes  in  from  above." 

"How  much  smaller  is  it?  "  said  James. 

"  It  is  not  more  than  half  as  large,"  said 
Rollo  ;  "  exactly  half  as  large ;  for  Jonas  bored 
the  large  hole  with  an  inch  auger,  and  the 
small  hole  with  a  half  inch  auger." 

"  Then  it  is  only  a  quarter  as  large,"  said 
Miss  Mary. 

"  Why,  Miss  Mary !  "  said  Rollo  ;  "  a  half 
an  inch  only  quarter  as  large  as  an  inch  !  "  and 
he  laughed  heartily  that  Miss  Mary  should 
have  made  such  a  mistake  in  her  mathema- 
tics. 

"  I  admit,"  said  Miss  Mary,  "  that  the 
small  hole  is  just  half  as  large  in  diameter  as 
the  large  hole ;  but  then  it  is  only  a  quarter 
as  large  in  area." 

f  11 


122  WATER. 

"  I  don't  know  what  you  mean,"  said 
James. 

"Why,  diameter  means  the  distance  across 
it,  and  area  means  the  whole  space.  Now, 
it  is  certainly  only  twice  as  far  across  the 
large  hole  as  it  is  across  the  small  hole ;  but, 
then,  the  space  is  four  times  as  great." 

"  Why  is  that  ?  "  asked  Hollo. 

"  Because,"  said  Miss  Mary,  "  the  large  hole 
is  not  only  twice  as  long,  but  it  is  twice  as 
broad  as  the  small  one.  You  can  understand 
it  better  by  supposing  two  square  boards.  If 
you  had  one  square  board  a  foot  long,  and  a 
foot  broad,  and  James  had  one  half  a  foot 
long  and  half  a  foot  broad,  yours  would  be 
four  times  as  large  as  his,  because  it  would 
be  twice  as  large  both  ways.  If  you  were 
to  saw  yours  in  two,  through  the  middle, 
each  half  would  make  two  like  James's." 

"Yes,"  said  Rollo,  "so  it  would.  But 
then  these  holes  are  not  square ;  they  are 
round;  and  that  might  make  some  differ- 
ence." 

"  No,"  said  Miss  Mary ;  "  it  makes  no  dif- 
ference. The  mathematicians  have  proved 
that  it  is  always  so  with  circles  as  well  as 
squares.  If  one  circle  is  twice  as  far  across 


BLOWING. 


123 


as  another,  it  is  four  times  as  large ;  or,  in 
mathematical  language,  if  the  diameter  is 
twice  as  great,  the  area  will  be  four  times  as 
great." 

"  Well,"  said  Rollo,  "  and  now  about  the 
plugs." 

:-Yes,"  replied  Miss  Mary,  "let  us  now 
reason  about  the  plugs.  The  small  hole  will 
only  let  through  a  quarter  part  as  much  wa- 
ter as  the  large  one,  with  the  same  pressure  ; 
and  of  course  there  must  be  four  times  as 
much  pressure  to  make  the  same  quantity  of 
water  pass. 

"Yes,"  said  Rollo,  "and  so  the  water 
must  rise  four  times  as  high." 

"  I  believe  so,"  said  Miss  Mary  ;  "  that  is, 
if  four  times  the  height  of  water  would  make 
exactly  four  times  the  pressure  ;  and  I  believe 
it  would.  Now,  I  think  the  water  cannot 
rise  four  times  as  high  without  going  over 
the  top  of  the  board,  and  of  course  you  can- 
not, with  this  dam,  get  a  pressure  sufficient 
to  carry  all  the  water  through  that  opening." 

"  It  is  running  over,"  interrupted  James ; 
"see,  it  is  running  over!  " 

It  was  beginning  to  run  over  a  little,  here 
and  there,  along  the  edge  of  the  board,  as 


124  WATER. 

James  said.  Jonas  had  oeen  careful,  when 
he  put  the  board  down,  to  make  the  upper 
edge  as  nearly  level  as  he  could  get  it ;  and 
then,  when  he  came  up  from  his  work,  the 
first  night  after  it  had  been  made,  he  stopped 
a  moment  to  look  at  it,  to  see  if  the  water 
was  running  over  it  equally.  He  found,  by 
the  running  of  the  water,  that  one  end  of  the 
board  was  a  little  higher  than  the  other,  and 
he  drove  it  down  a  little  with  his  axe  ;  and 
then  the  water  glided  over  the  edge  of  the 
board  in  one  regular  sheet,  of  equal  thickness 
from  end  to  end. 

And  now,  therefore,  when  the  water  began 
to  run  over,  it  began  in  various  places  all 
along  the  edge  of  the  board.  At  the  same 
time,  the  jet  from  the  small  hole  was  spout- 
ing away  with  very  considerable  force,  carry- 
ing off  a  large  portion  of  the  water,  but  not 
the  whole. 

"I  wish,"  said  Rollo,  "that  my  dam  was 
a  little  higher,  and  then  perhaps  the  water 
would  rise  high  enough  to  force  it  all  through 
the  small  hole." 

"  Couldn't  you  put  another  board  on  ?  "  said 
Miss  Mary. 

"  O  yes,"  said  Rolio,  jumping  up  and  clap- 


BLOWING.  127 

pmg  Ins  hands ;  "  we  will :  James,  we  will 
If  you  will  wait  here,  Miss  Mary,  for  u& 
James  and  I  will  go  up  immediately  and  ge 
another  board." 

Miss  Mary  promised  to  wait ;  and  so  Rollo 
and  James  set  off  towards  the  house.  They 
first,  however,  took  the  measure  of  the 
length,  so  that  the  board  should  fit  to  its 
place.  When  they  got  up  to  the  house,  they 
found  a  board  very  easily  ;  but  they  had  some 
difficulty  in  sawing  it  off,  neither  Rollo  nor 
James  being  much  accustomed  to  the  use  of 
the  saw.  Rollo  worked  upon  it  for  a  time, 
and,  when  he  was  tired,  he  gave  the  saw  to 
James.  However,  they  got  it  sawed  off  at 
length  ;  and  then  they  took  it,  one  boy  at 
each  end,  and  carried  it  down  to  the  dam. 
Then  they  placed  it  very  carefully  upon  the 
top  of  the  other  board,  pressing  it  down  hard 
upon  it,  and  letting  it  lean  back  against  the 
stakes  which  Jonas  had  driven  in,  and  which 
were  long  enough  to  support  this  additional 
board,  as  well  as  the  one  first  put  down. 
The  whole  operation  seemed  to  succeed 
perfectly. 

The  new  board  was  not  so  wide  as  the 
other ;  it  was  not  more  than  five  or  six 


128  WATER. 

inches  wide,  while  the  other  was  nearly  a 
foot.  Still  they  thought  it  would  be  wide 
enough. 

"  It  will  raise  the  water  half  a  foot,"  said 
Rollo,  "  and  that  will  put  a  great  deal  more 
pressure  on." 

But  they  found  that  the  two  boards  did 
r.ot  fit  together  very  well,  and  some  water 
escaped  through  the  crack  between  them. 
Rollo  endeavored  to  drive  the  upper  board 
down  closer  to  the  lower  one,  by  striking 
the  upper  edge  of  it  with  a  sort  of  club 
which  he  picked  up  upon  the  bank.  He  did, 
in  this  way,  make  the  junction  of  the  boards 
somewhat  closer,  but  still  some  water  would 
find  its  way  through. 

However,  notwithstanding  this,  they  soon 
found  that  the  water  was  slowly  rising  up 
the  side  of  the  upper  board ;  and  of  course, 
as  the  depth  increased,  the  pressure  increased 
too,  and  the  jet  of  water  from  the  hole  which 
was  near  the  bottom  of  it  was  thrown  out 
with  greater  and  greater  force.  They  all 
thought  that  probably,  before  the  water  got 
as  high  as  to  the  top  of  the  upper  board,  the 
pressure  would  be  great  enough  to  force  it  out 
as  fast  from  the  hole  as  it  came  in  from 


BLOWING.  129 

the  brook  above  ;  and  it  is  very  possible  thai 
it  might  have  been  so,  had  not  the  progress 
of  the  experiment  been  interrupted  in  a 
singular  manner.  The  dam  Mowed. 

And  this  was  the  way.  They  were  stand- 
ing together  near  the  bank,  looking  at  the  jet 
of  water,  which  was  spouting  away  beau- 
tifully to  a  considerable  distance  down  the 
stream,  when  James,  who  had  been  looking 
down  into  the  water,  said  suddenly,  — 

"  O  Hollo,  see  that  little  stick  sailing  round 
and  round." 

Hollo  looked  down  where  James  pointed, 
and  saw  a  small  stick  slowly  revolving  in 
the  water,  in  the  corner  near  one  end  of  the 
dam,  close  in  by  the  bank.  Both  Hollo  and 
Miss  Mary  watched  it  for  several  minutes, 
wondering  what  could  make  it  move  in  that 
curious  way.  The  stick  revolved  faster  and 
faster ;  and  presently  there  seemed  to  be  a 
small  depression  in  the  water,  and  a  little 
leaf,  which  was  floating  near,  began  to  move 
round  in  the  same  way. 

"It  is  a  little  whirlpool,"  said  Miss  Mary. 

"  Yes."  said  Rollo  ;  "  what  a  beautiful  little 
whirlpool.  What  makes  it,  Miss  Mary  ? >: 

"1   don't   know,"   said  Miss   Mary.      ''I 


WATER. 


have  often  seen  such  little  whirlpools  in  the 
water,  though  not  generally  in  such  still 
water  as  this." 

"  It  grows  bigger,"  said  Rollo. 

It  was  indeed  growing  a  little  bigger. 
The  depression  in  the  centre  became  deeper, 
and  the  little  sticks  and  leaves  were  whirled 
around  in  it  very  rapidly  —  phenomena 
which  seemed  to  puzzle  both  R^ollo  and  Miss 
Mary  a  good  deal,  until  their  surprise  was 
increased  by  a  discovery  which  Miss  Mary 
made  of  another  strange  appearance. 

Just  below  the  dam,  at  the  same  end  of  it, 
Miss  Mary  observed  a  strange  commotion  in 
the  sand,  and  a  sort  of  boiling  up  of  water 
like  a  boiling  spring. 

"  See,  children !  "  said  she  ;  "see  there  !  " 

"  What  is  it  ?  "  said  James. 

"  What  makes  it  ?  "  said  Rollo. 

"  0,  I  understand,  now,"  said  Miss  Mary. 
"  It  is  a  leak.  The  dam  has  sprung  a-leak. 
There  is  a  hole  underneath,  and  the  water 
goes  down  in  the  whirlpool,  and  then  comes 
boiling  up  on  the  under  side." 

"  So  it  is,"  said  Rollo.  "  But  I'll  stop 
it.  I'll  get  some  sand  on  my  spade,  and 
stop  it." 


BLOWING.  131 

•(  O  no,"  said  James ;  "  then  you'll  spoil 
the  whirlpool." 

"Well,"  said  Miss  Mary,  "it  is  better  to 
spoil  the  whirlpool  than  the  dam." 

"But  it  won't  spoil  the  dam,"  said  James. 
"  It  does  not  hurt  the  dam  at  al'.  It  makes 
it  prettier." 

"  But  it  will  wear  the  hole  out  bigger  and 
bigger,"  said  j\Jiss  Mary,  "  until  it  carries  the 
dam  all  away.  See,  it  is  growing  bigger  now 
very  fast ;  get  some  sand  and  gravel,  and  stop 
it  quick,  Rollo." 

Hollo  hastened  about,  trying  to  get  his 
spade  into  the  ground  here  and  there  to  get 
some  sand  or  earth  to  stop  the  leak  with ; 
but  the  greensward  was  so  tough,  and  there 
were  so  many  roots  of  trees  among  the  grass, 
that  he  could  not  get  any. 

"  Dig  here,  Rollo,"  said  James. 

James  pointed,  as  he  spoke,  to  the  sand 
and  gravel  in  the  bed  of  the  brook  below  the 
dam ;  and  Rollo  ran  there  with  his  spade, 
and  immediately  began  digging  with  his 
spade  among  the  loose  sand  and  gravel  which 
was  lying  there. 

"  Chuck  it  right  into  the  whirlpool,"  said 
Miss  Mary. 


WATER. 

"  Rollo  found  the  digging  very  easy,  and 
took  up  spadeful  after  spadeful  of  sand,  and 
threw  it  into  the  whirlpool.  In  a  few 
minutes,  however,  the  water,  which  had 
boiled  up  on  the  lower  side  of  the  dam,  be- 
gan to  be  so  abundant,  that  it  interfered  very 
much  with  his  digging.  The  jet  of  water, 
too,  spouting  from  the  hole,  was  in  his  way ; 
and,  besides,  he  was  soon  out  of  breath.  He 
accordingly  said  he  must  stop  to  rest  a 
minute,  and  he  stepped  out  upon  the  bank, 
and  they  all  looked  down  at  the  whirlpool  to 
see  whether  he  had  done  any  good. 

No ;  the  water  whirled  as  violently  as  ever, 
and  it  boiled  up  below,  they  thought,  with 
increased  force. 

"I  don't  believe  we  can  stop  it,"  said 
Rollo. 

"Here's  a  good  place  to  dig,"  said  Miss 
Mary.  She  pointed  to  a  projecting  bank  a 
little  way  up  from  the  dam,  where  the  earth 
seemed  soft,  and  pretty  free  from  grass  and 
roots. 

"Let  me  have  the  spade,"  said  James, 
"  and  you  rest,  Rollo." 

So  James  took  the  spade,  and  began  to  dig 
in  the  bank.  It  was  pretty  easy  digging,  but 


BLOWING.  133 

James  was  not  quite  strong  enough  to  throw 
the  spadeful  of  earth  so  far.  The  first  spade- 
ful stuck  to  the  spade  a  little,  and  fell  into  the 
middle  of  the  dam.  The  second  fell  a  little 
short  of  the  whirlpool,  where  it  could  do  but 
little  good.% 

"  Let  me  have  the  spade,"  said  Miss  Mary  j 
"  I  can  dig." 

Miss  Mary  was  so  much  interested  in  sav- 
ing the  dam,  that  she  wanted  to  try ;  but  she 
did  not  succeed  much  better  than  the  boys. 
She  had  to  crowd  the  spade  into  the  earth 
by  the  strength  of  her  arms,  instead  of  press- 
ing it  down  with  her  foot,  as  the  boys  had 
done  ;  for  her  shoes  were  too  light  and  thin 
for  such  a  purpose.  In  her  attempt,  therefore, 
to  use  a  spade,  she  made  somewhat  such  a 
figure  as  a  boy  makes  in  attempting  to  sew 
without  a  thimble. 

However,  she  accomplished  something. 
She  threw  several  pretty  good  spadefuls 
directly  into  the  mouth  of  the  whirlpool,  and 
Rollo  though  t  that  they  would  certainly  stop 
the  leak.  Instead  of  that,  however,  the  vor- 
tex seemed  to  swallow  them  up  in  an  instant, 
and  itself  to  grow  larger  and  larger  continu- 
ally. 

12 


134  WATER. 

"Il's  of  no  use,"  said  Hollo,  at  length; 
"  and,  in  fact,  I  remember  that  Jonas  said  it 
would  do  no  good  to  shovel  in  sand  and 
gravel  with  ten  inches  head  on." 

"  Head  on  !  "  repeated  Miss  Mary. 

"  Yes,  head  of  water,"  said  Rollo. 

"  O,  he  meant  the  pressure  of  the  ten 
inches  of  water." 

"  Yes,"  said  Rollo. 

"I  forgot  that,"  said  Miss  Mary.  "The 
hole  is  down  at  the  very  bottom,  and  so  there 
must  be  a  great  pressure.  The  pressure 
drives  the  water  through  the  leak  with  as 
much  force  as  it  does  through  the  hole,  and 
that  carries  every  thing  that  we  throw  in  right 
through." 

"  Only  see  how  the  water  has  fallen,"  said 
Rollo. 

It  had  fallen  very  much  indeed.  It  was 
below  the  top  of  the  lower  board,  and  was 
fast  settling  lower  still.  The  jet  from  the 
hole  in  the  board  had  very  much  diminished 
in  force,  but  it  was  still  flowing.  The  whirl- 
pool had,  however,  become  very  large,  as  large 
round,  and  almost  as  deep,  as  a  water-pail ; 
and  the  water,  with  great  quantities  of  sand 
and  gravel,  came  boiling  up  on  the  lowei 


BLOWING. 

side.  They  saw  very  plainly  that  u  mon- 
strous hole  had  been  made  under  and  around 
the  end  of  the  board,  which  it  would  require 
a  great  deal  of  gravel  to  stop  again. 

"  We  never  can  stop  it,  in  the  world,"  said 
Rollo. 

"  Jonas  can,"  said  James. 

"  I  am  not  certain  that  you  cannot  mend 
it  yourselves,"  said  Miss  Mary. 

"O  Miss  Mary,"  said  Rollo,  "if  we 
couldn't  stop  it  when  it  first  began,  and  was 
small,  we  certainly  can't  stop  it  now." 

"  Why,  then  the  pond  was  full,"  said  Miss 
Mary,  "  and  there  was  a  great  pressure  upon 
it ;  but  now,  after  the  water  is  all  out,  and 
there  will  be  no  pressure,  you  can  fill  up  the 
hole  by  wheeling  in  earth  with  your  wheel- 
barrow, perhaps." 

"  Perhaps  we  can,"  said  Rollo,  despond- 
ingly ;  "  but  I  think  that  Jonas  can  mend  it 
better." 

They  all  stood  for  several  minutes,  gazing 
in  silence  upon  the  ruins  of  the  dam,  as  the 
last  of  the  water  poured  out  through  the  great 
opening  which  the  pressure  of  the  water  had 
made.  At  last  Miss  Mary  said,  — 


136  WATER. 

"  Well,  boys,  I  am  sorry  that  the  dam  is 
gone." 

"  So  am  I,"  said  Hollo.  "  It  is  because  I 
put  on  the  upper  board." 

"  I  think  it  very  likely,'1  said_  Miss  Mary  ; 
"  that  increased  the  pressure,  so  as  to  force  a 
hole  through  under  the  board." 

"I  expect  that  is  what  Jonas  meant  by 
blowing.  It  is  a  strange  sort  of  a  name, 
'seems  to  me." 

"  It  is  a  strange  sort  of  a  thing,"  said  Miss 
Mary,  "  'seems  to  *me.  But,  at  any  rate,  we 
have  all  learned  something  about  the  pressure 
of  water  by  it." 

"Yes,"  said  Hollo.  "I'll  tell  Jonas  all 
about  it  when  I  get  home." 

Here  Miss  Mary  bade  the  children  good 
by ;  and  she  went  home  her  way,  and  they 
went  theirs. 


QUESTIONS. 

How  did  Miss  Mary  make  the  appointment  to  meet 
Hollo  and  James  ?  What  did  the  boys  find  the  state  of  the 
dam  when  they  went  to  it  ?  Was  the  water  running  over  ? 
When  they  pulled  out  the  large  plug,  did  it  at  fi»»t  dia« 


BLOWING.  137 

charge  the  water  as  fast  as  it  came  in  ?  Did  it  cause  ttie 
water  to  subside  ?  Did  it  continue  to  subside  as  long  as 
the  boys  expected  ?  What  question  did  they  have  ready 
to  propose  to  Miss  Mary  when  she  came  ?  What  experi- 
ments did  they  perform  in  presenting  their  question  ?  How 
did  Miss  Mary  explain  the  difficulty  ?  Why  could  not  the 
boys  get  the  small  plugs  out?  What  was  the  design  of  the 
boys  in  raising  the  dam  by  another  board  ?  What  was  the 
first  indication  that  the  water  had  forced  a  hole  under  the 
dam  ?  Describe  the  efforts  which  they  made  to  stop  it. 

f*          n* 


CHAPTER    IX. 

BRIDGE   BUILDING. 

ROLLO  could  not  tell  Jonas  about  the  dam 
that  night,  because  he  had  gone  away,  and 
was  not  to  come  home  until  after  Hollo  had 
gone  to  bed.  He,  however,  told  his  father  all 
about  it.  He  described  to  him,  first,  how 
they  had  drawn  off  the  water  from  their  dam, 
with  their  plugs,  and  the  explanations  which 
Miss  Mary  had  made  of  the  principle, — 
namely,  that  the  water  would  rise  until  the 
pressure  was  great  enough  to  force  it  through 
the  hole  as  fast  as  it  would  come  in  from 
above. 

"  Yes,"  said  his  father,  "  Miss  Mary  was 
correct ;  and  that  is  a  very  important  princi- 
ple. It  explains  an  effect  which  we  have 
seen  taking  place  a  thousand  times." 

"O  father,"  said  Hollo,  "I  never  saw  it 
before." 

"  You  never  observed  it  before,  you  mean,' 
replied  his  father. 


BRIDGE    BUILDING.  139 

"  No  sir,  I  never  saw  it  before.  I'm  sure 
I  never  saw  a  brook  dammed  up  before  with 
a  board,  so  as  to  make  all  the  water  rnn 
through  a  little  round  hole." 

"  Suppose  the  hole  had  been  a  square  hole , 
would  it  not  have  been  the  same  thing  ? " 
asked  his  father. 

"  Yes,  sir,"  said  Hollo.  "  The  shape  of  the 
hole  makes  no  difference.1' 

"  And  suppose,  instead  of  a  board,  it  had 
been  a  great  flat  stone,  with  a  hole  drilled 
through  it  ? " 

"  Just  the  same,"  said  Hollo. 

"  Or  two  stones,"  continued  his  father, 
"  with  a  narrow,  confined  place  between 
them?" 

"  Then  you  could  not  plug  it  up,"  said 
Rollo. 

"  But  plugging  it  up  has  nothing  to  do 
with  the  effect  produced  while  it  is  open. 
Your  apparatus  was,  in  fact,  essentially,  only 
a  partial  obstruction  to  the  stream.  Had 
there  been  no  opening  for  the  water,  it  would 
have  been  a  total  obstruction.  As  it  was,  it 
was  a  partial  obstruction.  There  was  a  con- 
fined and  narrow  passage  for  the  water." 

"  Yes,  sir,"  said  Rollo,  "  a  half-inch  hole.J 


140  WATER. 

"  Now,  the  same  principle,  which  governed 
the  motion  of  the  water,"  said  his  father,  "  in 
the  case  of  the  artificial  obstruction  which 
you  made,  governs  it  in  the  case  of  the  nat- 
ural obstructions  formed  along  the  bed  of  the 
brook,  by  narrow  banks  or  stones ;  so  that, 
by  walking  along  the  brook  with  you,  some 
day,  I  could  perform  precisely  the  same  ex- 
periment, and  in  fact  show  it  to  you,  as  per- 
formed by  nature  before  you,  in  many  places." 

"  O  father,"  said  Rollo,  "  I  wish  you 
would." 

"  I  will,  some  time  when  I  am  at  leisure. 
Or  you  can  do  it  for  yourself,  and  show  James 
and  Miss  Mary." 

"  But  I  don't  think  I  can  find  the  places,  ' 
said  Rollo. 

"  O  yes,"  said  his  father,  "  find  any  places 
where  there  are  obstructions.  There  is  one 
place  I  recollect,  just  above  where  you  dug 
up  a  little  pine-tree.  There  are  two  great 
stones,  or  rocks,  leaning  against  each  other, 
with  a  narrow  passage  between  them." 

"  Yes,  sir,"  said  Rollo,  "  where  James  and 
I  always  step  over,  —  except  when  there  is  a 
treshet." 

"  Now,  that,"  continued  his  father,  '  is  a 


BRIDGE    BUILDING.  141 

narrow  and  confined  place,  and  the  water 
cannot  come  through  as  fast  as  it  cornes 
down  from  above." 

"  It  can  now,"  said  Rollo. 

"  Then  it  is  because  the  water  is  very 
low,"  said  his  father. 

"  Yes,  sir,"  said  Rollo,  "  the  water  is  very 
low." 

"  But  when  the  brook  is  as  full  as  usual, 
it  is  too  small.  All  the  water  cannot  get 
through  without  an  extra  pressure  upon  it  to 
force  it.  So  you  will  find,  if  you  examine 
the  place  at  some  time  when  a  good  deal  of 
water  is  running,  that  the  surface  of  the  water 
above  the  obstruction  will  be  considerably 
higher  than  it  is  below.  The  reason  is,  as 
Miss  Mary's  experiment  shows  very  satis- 
factorily, that  the  water  cannot  all  get  through 
without  running  a  great  deal  faster  than  it 
does  in  other  parts  of  the  brook,  where  it  has 
more  room.  And  it  will  not  run  any  faster 
unless  it  is  forced  to,  by  a  pressure  from 
behind ;  and  thus  the  water  behind  accumu- 
lates and  rises  until  it  furnishes  a  pressure 
sufficient  to  force  the  water  through  the 
narrow  place." 

"  Yes.  sir,"  said  Rollo,  "  I  remember  that 


142  WATER. 

there  is  a  deep  place  above  the  rocks,  —  a 
kind  of  a  pond."' 

"And  always,"  continued  Hollo's  father, 
"  any  obstruction  whatever  in  a  brook  or 
river,  whether  by  shallows,  or  rocks,  or  pro- 
jecting banks,  or  a  narrow  bed,  raises  the 
water  above  the  obstruction.  The  piers  of  a 
bridge  are  a  remarkable  instance." 

"  What  are  the  piers  of  a  bridge  ? "  said 
Hollo. 

"  Why,  when  people  build  a  bridge,  they 
have  to  build  up  some  stone  work  upon  the 
banks,  on  each  side,  to  support  the  ends  of 
the  bridge.  These  are  called  abutments. 
Then,  besides,  if  the  river  is  wide,  they  gen 
erally  have  to  build  some  supuorts  for  the 
middle  of  it." 

"  What,  right  in  the  water  ?  "  said  Hollo. 

"  Yes,  and  these  are  called  piers.  In  stone 
bridges,  across  wide  rivers,  there  are  a  great 
many  piers ;  and  the  road  way  goes  across 
from  one  to  the  other,  over  arches.  In 
wooden  bridges,  they  do  not  have  so  many 
piers,  because  the  long  beams  will  extend 
pretty  far.  But,  in  all  cases,  every  pier  which 
is  built  upon  in  a  river,  takes  away  from 
some  of  the  space  that  the  river  had  to  flow 


BRIDGE    BUILDING.  143 

in,  and  so  narrows  the  channel.  Now,  every 
body  that  has  observed  the  effect  of  bridges, 
knows  that  this  always  makes  the  water 
above  the  bridge  stand  at  a  higher  level  than 
it  did  before ;  —  but  every  body  does  not 
know  what  the  principle  is  which  regulates 
the  height  of  this  level.  Can  you  tell  me 
what  it  is  ?  " 

"Yes,  sir,"  said  Rollo ;  '"it  rises  till  there 
is  pressure  enough  to  force  the  water  through 
between  the  piers." 

"  Yes,"  said  his  father,  "  and  there  is  great 
advantage  in  knowing  the  principle,  for  then 
they  can  calculate  from  it  how  great  the  rise 
will  be." 

"  How  ?  "  said  Rollo. 

"  Why,  first,"  replied  his  father,  "  they 
calculate  how  much  the  piers  diminish  the 
space  which  the  water  had  to  pass  in.  Then 
from  that  they  can  tell  how  much  swifter  it 
must  pass  in  order  to  go  through  in  the  same 
time.  Then  they  can  calculate  how  much 
the  water  must  rise  to  give  a  sufficient  pres- 
sure to  effect  this." 

"  Yes,"  said  Rollo,  "  Miss  Mary  calculated 
how  high  the  water  must  rise  before  it  could 
go  out  fast  enough  through  our  small  hole." 


144  WATER. 

"  That  is  the  advantage  of  understanding 
principles  as  well  as  learning  facts,"  said  his 
father.  "  Understanding  principles  enables 
us  to  make  calculations.  But  now  you  must 
go  and  amuse  yourself.  I  cannot  talk  with 
you  any  more." 

"  Well,  father,  only  just  tell  me  one  thing. 
How  is  it  that  they  can  build  piers  out  in  the 
middle  of  a  river  ?  " 

"  O,  there  are  several  ways  of  building  be- 
low the  surface  of  the  water,"  said  his  father. 
"  One  way  is  by  a  diving-bell." 

"  A  diving-bell  ?  "  repeated  Rollo. 

"  Yes ;  that  is  a  large,  heavy  apparatus, 
shaped  like  a  bell,  but  large  enough  to  hold 
two  or  three  men.  Then  it  is  let  down  into 
the  water,  mouth  downwards." 

"  Why,  father,  the  man  would  fall  out,  and 
sink  to  the  bottom." 

;<  O,  they  have  a  kind  of  shelf  across  for 
the  man  to  sit  upon,  and  another  for  his 
tools,"  said  his  father,  "and  so  they  lower 
him  down  to  the  bottom  of  the  water.  The 
air  in  the  diving-bell  is  for  him  to  breathe. 
Then,  when  the  man  is  down  near  the  bottom, 
Ili3y  can  lower  a  stone  down  to  him,  and  let 


BRIDGE    BUILDING. 

him  guide  it  exactly  into  the  place  where  it 
ought  to  go." 

"  What  is  another  way  ?  "  said  Rollo. 

"Another  way,"  said  his  father,  "is  to 
drop  large  stones  into  the  water  all  over  the 
place  where  the  pier  is  to  be,  and  thus  fill  up 
to  the  surface ;  and  when  they  have  got  a 
large  place  filled  up  to  the  surface  of  the 
water,  then  they  can  begin  to  place  the 
stones  regularly." 

"  That  is  the  easiest  way,"  said  Rollo. 

"Yes,"  said  his  father;  "but  then  it 
wastes  the  stone ;  because  the  stones  that 
are  dropped  in,  spread  out  in  every  direction 
over  the  bottom  of  the  water,  and  so  a  great 
many  more  are  required  than  would  be  neces- 
sary if  they  were  built  up  perpendicularly, 
upon  a  foundation  no  larger  than  the  pier 
itself  was  to  be. 

"  And  besides,  there  is  another  difficulty," 
continued  Rollo's  father.  "  The  stones  thus 
spreading  out  in  every  direction  occupy  a 
great  deal  of  the  space  under  water  between 
the  piers,  so  that  the  water  has  less  room  for 
its  flowing.  Of  course  the  water  will  rise 
much  higher  above  the  bridge,  on  account 
of  this  increased  obstruction.  For,  according 

t  13 


140  WATER. 

to  our  principle,  it  must  rise  high  enough  to 
produce  a  pressure  sufficient  to  force  all  the 
water  through  or  over  the  obstructions." 

"  Well,  sir,"  said  Rollo,  "  and  what  harm 
docs  it  do  for  the  water  to  rise  ? " 

"  Why,  it  might  overflow  the  land  above, 
especially  the  intervals  and  meadows.  Then, 
in  high  floods,  Ji  the  spring  of  the  year,  when 
the  ice  is  coming  down,  it  might  rise  high 
enough  for  the  ice  or  floating  timber  to  strike 
the  bridge  itself,  and  carry  it  away  off  from 
the  piers.  Then,  besides,  the  more  obstruc- 
tion there  is  between  the  piers,  the  more 
rapid  the  current  must  be ;  for,  if  it  has  a 
narrow  or  a  shallow  place  to  go  through,  it 
must  go  through  so  much  the  quicker ;  and 
this  would  prevent  boats  coming  up  under 
the  bridge,  and  make  it  dangerous  for  them 
to  go  down." 

"  There  seems  to  be  a  great  many  diffi- 
culties," said  Rollo. 

"  Yes,"  said  his  father ;  "  and.  so  engineers 
always  consider  it  very  important,  in  build- 
ing bridges,  to  obstruct  the  passage  of  the 
water  as  little  as  possible.  Every  thing  they 
do  must  obstruct  it  in  some  degree.  Even  a 
single  post  put  in,  to  support  the  middle  of  a 


BRIDGE    BUILDING.  14? 

bridge  nariows  the  channel  for  the  passage 
of  the  water,  and  so  prevents  a  part  of  thft 
water  from  passing,  until  it  rises  enough 
above,  to  put  on  a  sufficient  pressure  to  force 
it  through  enough  quicker  to  make  up  for  the 
narrowness  of  the  space." 

"  I  should  not  think  one  post  would  make 
any  difference,"  said  Hollo. 

"  It  would  not,  probably,  make  any  sensible 
difference,"  said  his  father,  "but  it  must 
make  a  real  difference ;  for,  if  one  post  did 
not  make  any  difference  at  all,  another  might 
be  put  in,  without  making  any,  and  another, 
arid  another  f^and  thus  a  whole  row  of  posts 
might  be  put  in,  extending  from  bank  to 
bank,  without  making  any  obstruction.  The 
fact  is,  that  any  obstruction  whatever  must 
raise  the  water  above  it  in  the  proportion  which 
the  obstruction  bears  to  the  whole  breadth 
of  the  river.  Therefore,  in  building  bridges 
over  running  streams,  they  are  always  very 
careful  to  make  as  little  obstruction  as  possi- 
ble. They  make  as  few  piers  as  will  answer 
to  support  the  bridge,  so  as  to  have  as  wide 
spaces  between  them  as  they  can.  They 
make  them  as  narrow,  too,  as  they  can  ;  arid 


148  WATER. 

they  build  them  up  compact  and  solid  from 
the  bottom." 

"  Then  it  won't  do  to  tumble  the  stones 
in."  said  Rollo. 

"  No,"  replied  his  father,  "  they  can  only 
do  that  in  lakes  and  in  the  sea,  when  they 
want  to  build  a  lighthouse,  or  a  mole,  or  a 
breakwater." 

"  A  mole  ?  "  said  Rollo  ;  "  what  is  a  mole  ?  " 

"  Why,  I  can't  tell  you  about  a  mole 
.now  very  well,"  said  his  father ;  "  I  have 
spent  more  time  now  in  talking  to  you  than 
I  could  well  spare." 

"  Well,  father,  then  you  need  not  tell  me 
any  more ;  only  there  was  another  way  of 
building  foundations  under  water,  that  you 
did  not  tell  me  of.  But  that  will  do  as  well 
some  other  time,  if  you  want  to  be  busy 
now." 

"No,"  replied  his  father,  "I  will  tell  you 
about  that  now,  as  it  will  only  take  me  a 
minute  or  two.  It  is  by  what  they  call  a 
coffer  dam." 

"  I  never  heard  of  a  coffer  dam "  said 
Rollo 

"No,   probably   not,"  replied  his   father 


BRIDGE    BUILDING.  14& 

"  The  way  they  make  a  coffer  dam  is,  by 
driving  two  rows  of  piles,  at  a  little  distance 
from  each  other,  into  the  bottom  of  the  river, 
all  around  the  place  where  the  pier  is  to  be 
built.  Then  they  fill  up  the  space  between 
these  rows  with  earth  or  clay.  This  makes 
a  tight  wall  all  around  the  place  where  they 
want  to  work.  Then  they  can  pump  out 
the  water  from  inside  this  wall,  or  coffer  dam. 
as  they  call  it." 

"  What  makes  them  call  it  a  coffer  dam  ?  " 
said  Rollo. 

"  Why,  coffer  means  box  or  chest ;  and  it 
is  a  sort  of  box  dam,  enclosing  a  certain  space 
all  around." 

"  And  so  they  have  a  good,  dry  place  to 
work  in,"  said  Rollo. 

"  Yes,"  replied  his  father ;  "  though  they 
may  have  water  all  around  them,  ten  or 
fifteen  feet  high." 

"  I  should  like  to  see  a  coffer  dam,"  said 
Rollo. 

"  You  would  be  very  much  interested  in 
seeing  one,  I  have  no  doubt,"  said  his  father 
"  But  this  is  all  I  can  tell  you,  now,  aboui 
working  under  water." 
13* 


150  WATER. 


QUESTIONS. 

What  did  Hollo's  father  say  about  the  principle  which 
Miss  Mary  had  explained  ?  Had  he  ever  himself  observed 
the  operation  of  it  ?  In  what  sort  of  cases  ?  What  'a 
always  the  effect  of  narrowing  or  obstructing  a  stream,  in 
respect  to  the  level  of  the  water  above  it?  What  is  an 
abutment  in  bridge  building  ?  What  is  a  pier  ?  What 
effect  do  the  piers  of  a  bridge  have  upon  the  level  of  the 
water  above  ?  What  effect  do  they  produce  upon  the  cur- 
rent ?  How  many  ways  did  Rollo's  father  mention  of 
laying  foundations  under  water?  What  was  the  first 
mode  ?  What  was  the  second  mode  ?  Is  this  second 
mode  suitable  for  the  piers  of  bridges  ?  Why  not  ?  In 
what  cases  is  it  suitable  ?  What  is  the  third  mode  men* 
tioned  ? 


CHAPTER    X. 

MOMENTUM. 

BESIDES  the  pressure  of  water,  there  is  also 
its  momentum.  Pressure  is  the  steady  force 
which  it  exerts  by  its  weight.  Momentum 
is  the  force  of  its  impulse,  when  it  is  in 
motion.  The  waves  of  the  ocean  dashing 
against  a  ship  in  a  storm,  furnish  an  ex- 
ample of  momentum.  The  water  spouting 
up  through  a  leak  in  the  bottom  of  a  ship,  is 
forced  upward  by  pressure.  A  brook  may 
destroy  a  dam  by  the  momentum  of  the  wa- 
ter, as  well  as  by  its  pressure.  This  Hollo 
learned  in  the  manner  to  be  described  in  this 
chapter. 

When  he  left  his  father,  he  went  away,  in- 
tending, the  next  time  he  saw  Jonas  again,  to 
ask  him  whether  they  could  not  make  a  cof- 
fer dam,  some  how  or  other,  around  the  hole 
in  their  dam,  and  so  get  a  better  opportunity 
to  repair  the  breach. 

He  went  out  into  the  back  yard,  wishing 


1 52  WATER. 

that  Jonas  was  at  home ;  but  he  had  not 
come.  Rollo  found,  too,  that  it  looked  like 
rain.  He  was  glad  of  it,  he  said  to  himself, 
as  it  would  make  the  brook  higher,  and  so 
the  water  would  spout  out  more  swiftly 
from  their  jets.  Rollo  was  mistaken,  how- 
ever, in  this  opinion.  He  forgot  that  the 
force  of  the  jet  depended  upon  the  height  of 
the  dam,  and  not  upon  the  quantity  of  water 
which  came  down  the  brook.  The  surplus 
water,  in  case  of  a  flood  in  the  brook,  would 
all  flow  over  the  top  of  the  board,  without 
much  affecting  the  pressure  on  which  the 
force  of  the  jet  depended. 

However,  Rollo  was  very  glad  to  see  it 
looking  like  rain;  and  he  was  still  more 
pleased,  a  few  minutes  afterwards,  at  feeling 
a  little  drop  falling  upon  his  cheek. 

That  night,  when  he  went  to  bed,  Rollo 
looked  out  of  the  window,  and  found  that  it 
was  raining  very  fast ;  and  he  determined  that 
he  would  get  up  early  the  next  morning,  and 
go  down  and  see  how  his  dam  appeared. 
He  thought  it  possible,  that,  when  the  brook 
was  full,  the  water,  coming  down  in  a  torrent, 
might  perhaps  wash  new  sand  and  gravel  into 
the  hob  which  had  been  made,  and  so  mend 


MOMENTUM.  153 

the  dam  itself.  He  determined  that,  at  any 
rate,  he  would  go  and  see. 

The  next  morning,  when  he  awoke,  it  was 
still  raining.  He  got  up,  and  dressed  himself, 
and,  when  he  came  down  stairs,  he  inquired 
how  .ong  it  would  be  before  breakfast. 
They  told  him  about  half  an  hour.  He  con- 
cluded, therefore,  that  he  would  wait  until 
after  breakfast,  for  he  wanted  a  little  more 
time  than  that. 

After  breakfast,  he  went  up  into  the  garret, 
where  he  used  to  keep  what  he  called  his 
weather  rigging.  This  weather  rigging  con- 
sisted of  clothes  for  him  to  wear  out  in  the 
storms.  He  used  often  to  like  to  take  walks 
out  in  the  storms  to  see  the  torrents,  and  the 
floods  in  the  brook,  and  the  great  pools  of 
water.  His  mother  allowed  him  to  go  out 
on  such  excursions,  provided  that  he  would 
get  Jonas  to  find  something  which  would 
protect  his  common  clothes  from  the  mud 
and  water. 

Accordingly  Jonas  had  ransacked  the  garret, 
and  found  an  old  great  coat  and  an  umbrella, 
also  a  straw  hat,  with  a  monstrous  broad  brim, 
which  Jonas  painted  so  as  to  make  it  imper- 
vious to  water.  He  also  had  a  pair  of  boots, 


154  WATER. 

old  and  patched,  but  still  tight,  and  they 
were  kept  water-proof  by  a  kind  of  composi- 
tion which  Rollo  used  to  put  on  them  with 
a  brush,  when  they  were  dry. 

All  this  Rollo  used  to  call  his  weather 
rigging;  and  he  told  his  mother  that  the 
very  pleasantest  walks  he  had  at  any  time, 
were  those  he  made  in  the  great  rain  storms, 
protected  by  his  weather  rigging. 

On  this  occasion,  Rollo  rigged  himself,  as 
usual,  for  a  storm  excursion ;  and,  with  his 
umbrella  over  his  head,  he  sallied  forth  into 
the  rain.  He  found  that  the  brook  had  risen 
considerably,  but  far  less  than  he  had  expect- 
ed. He  proceeded  slowly  and  cautiously ; 
for,  although  he  was  impatient  to  see  what 
effect  the  water  had  produced  upon  his  dam, 
he  knew  that  the  paths  were  slippery,  and  it 
required  some  care  and  circumspection  to  go 
safely. 

When  he  reached  the  dam,  he  found  that 
the  water  was  pouring  over  the  board  in  a 
torrent,  —  so  full  and  turbid  that  the  board 
was  entirely  concealed  from  view.  He  could 
see  the  top  of  the  stakes,  but  the  narrow 
board  which  they  had  placed  over  the  other 
seemed  not  to  be  there.  He  knew,  however 


MOMENTUM.  155 

that  the  lower  board  was  still  there,  for  there 
was  a  great  waterfall  at  the  place,  which  he 
thought  could  be  produced  only  by  the 
board's  keeping  its  position. 

There  was  a  great  whirl  and  boiling  of  the 
water  below  the  dam,  and  Rollo  looked  at  it 
very  carefully  to  see  if  he  could  ascertain,  by 
the  appearance  of  it,  whether  the  water  passed 
under  the  board,  as  well  as  over  it.  But  he 
could  not  tell.  There  were  no  signs  of  the 
whirlpool  above,  however,  and  Rollo  could 
not  help  hoping  that  the  flood  had  come  and 
filled  up  the  opening  which  the  pressure  of 
the  water  in  the  dam  had  made. 

Rollo  walked  up  the  brook  a  little  way, 
and  was  very  much  interested  in  observing 
the  various  appearances  which  the  foaming 
and  boiling  torrent  assumed  in  various  parts 
of  its  course,  according  to  the  nature  of  the 
bank.  In  one  place,  the  whole  force  of  the 
stream  dashed  against  a  rock,  which  stood 
firmly  in  the  very  centre  of  the  channel.  In 
another  place,  it  plunged,  with  many  a  whirl- 
ing eddy,  around  a  sharp  curve,  made  by  the 
bed  of  the  stream.  Here  its  course  was 
almost  choked  up  by  sticks  and  brush- wood, 
which  had  drifted  down,  and  caught  in  some 


156  WATER. 

narrow  part  of  the  channel;  and  there  it 
would  shoot  down  a  long,  unobstructed  de- 
scent, making  a  beautiful  cascade. 

Hollo  remained  for  half  an  hour,  watching 
the  swift  motions  of  the  water  in  these  and 
many  other  places ;  and  then  he  went  home. 
He  remained  at  home  until  noon.  After 
dinner,  he  looked  out  of  the  window,  and 
found  it  still  raining.  He  then  went  to  his 
book-case,  and  began  looking  over  books, 
with  his  little  brother  Nathan,  where  he 
became  so  much  interested  that  he  did  not 
think  much  about  the  weather,  until  a  little 
after  two  o'clock,  when  who  should  come  in 
but  James. 

"  Why,  James !  "  said  Hollo,  "  are  you  out 
in  all  this  rain  ?  " 

"Rain!"  repeated  James.  "It  does  not 
rain ;  it  is  all  clearing  away." 

"  Clearing  away  !  "  said  Rollo,  jumping 
up  from  his  books ;  "  then  let  us  go  down 
and  look  at  our  dam." 

"  Yes,"  said  James,  "  that  is  what  I  came 
for." 

"  O,  let  me  go  too,"  said  Nathan. 

"No,"  replied  Rollo,  "you  cairt  go,  Na- 
lhan  ;  it  is  very  wet  *nd  muddy." 


MOMENTUM.  157 

"  We  can  draw  him  in  his  wagon,"  said 
James. 

"Well,"  said  Hollo,  "if  mother  will 
let  you  go,  Nathan ;  go  and  ask  her." 

Nathan  ran  off  to  ask  his  mother,  and 
his  mother  said  that  he  might  go.  Most 
mothers  would  not  have  been  willing  to  let 
so  young  a  child  go  out  under  the  care  of 
two  such  boys  as  Hollo  and  James.  But 
Rollo  was  always  so  careful  to  keep  him 
from  getting  wet  and  muddy,  in  such  cases, 
that  she  generally  consented. 

So  they  put  Nathan  into  a  little  cart  or 
wagon  which  he  had,  and  Rollo  and  James 
drew  him  along.  They  found  that  the 
clouds  were  all  breaking  away,  and  the  sun 
coming  out.  It  had  not  rained  any  for 
nearly  an  hour,  so  that  the  water  had  run  off 
from  the  roads  and  paths.  As  they  walked 
along,  they  talked  together  thus  ;  — 

"  I  went  down  this  morning,  James,"  said 
Rollo,  "  and  the  brook  was  a  real  torrent.     I 
wish  you  could  have  seen  it  then." 
.  "  1  expect  it  will  be  a  real  torrent  now," 
said  James. 

"  Not  so  much  of  a  torrent  as  it  was  when 
J  saw  it,"  said  Rollo. 


158  WATER. 

"  Why  not  ? "  said  James. 

"Because,"  said  Rollo,  "it  does  not  rain 
now.  It  rained  very  fast  when  I  went  down 
this  morning." 

"  Hark  !  "  said  James;  "  I  hear  something 
roaring  down  in  the  woods." 

"What  is  it?"  said  Rollo. 

"  I  am  afraid  it  is  a  bear,"  said  Nathan. 

"A  bear!"  repeated  Rollo,  with  a  laugh ; 
"you  need  not  feel  afraid  of  a  bear,  Nathan, 
in  our  woods." 

"It's  the  brook,  Rollo,"  said  James;  "1 
believe  it  is  the  brook." 

"Yes,"  said  Rollo,  "it  is;  how  it  roars ! 
[  don't  think  it  roared  quite  so  much  when  I 
went  down  this  morning." 

The  boys  went  on  the  faster  after  they 
heard  the  roaring  of  the  brook  ;  and  when 
they  first  came  in  sight  of  it,  Rollo  admitted 
that  it  was  a  great  deal  higher  than  it  was 
when  he  saw  it  in  the  morning.  It  roared 
and  tumbled  along  with  tremendous  violence. 
Rollo  forgot,  when  he  spoke  as  if  the  water 
might  be  expected  to  be  the  highest  during 
the  continuance  of  the  rain,  that  it  takes 
some  time  for  the  water  which  comes  to  the 
earth  from  the  clouds,  to  find  its  way  down 


MOMENTUM.  159 

all  the  little  rivulets  and  streams  into  the 
brook,  and  that,  consequently,  the  water 
in  the  brook  will  be  highest  a  short  time 
after  the  rain  is  over. 

In  one  place  the  water  had  overflowed  the 
banks  of  the  brook,  and  had  spread  all  about 
under  the  trees,  which  thus  seemed  to  be 
growing  out  of  a  pond.  The  rock  which 
Hollo  had  observed,  in  the  morning,  breasting 
the  torrent,  was  now  wholly  under  water, 
and  the  stream  showed  no  indication  of  its 
presence,  except  by  a  ripple.  The  boys 
noticed  these  things  as  they  passed,  but  they 
hastened  along  to  the  dam  to  see  what  were 
the  appearances  there. 

They  could  see  no  traces  of  the  dam 
whatever.  The  water  swept  over  the  place, 
in  one  overwhelming  and  unbroken  torrent. 
The  boys  stood  upon  the  bank  a  few  min- 
utes, looking  on  in  silence,  and  yet  with  great 
interest,  until  at  length  James  said,  — 

"  It  is  all  carried  away,  isn't  it,  Rollo  ? " 

"  I  don't  know,"  answered  Rollo,  "  whether 
it  has  been  carried  away,  or  whether  it  13 
all  there. — deep  under  water." 

"  But  the  stakes,  Rollo,  the  stakes !  The 
stakes  could  not  be  covered  with  water. 


160  WATER. 

And  so,  if  the  dam  was  there  still,  we  should 
see  the  tops  of  the  stakes !  " 

Rollo  did  not  reply,  but  he  considered 
James's  reasoning  as  unanswerable. 

"  Then,"  said  he,  after  a  short  pause,  "the 
stakes  and  the  board  have  all  gone  down 
stream  together,  and  that's  the  end  of  our 
dam." 

"  However,"  he  continued,  "  at  any  rate, 
if  we  have  not  got  a  dam,  we  have  got  a 
cataract,  and  we  will  sail  some  ships  down." 

So  the  boys  left  Nathan  in  the  wagon,  in 
a  place  where  he  could  see  pretty  well,  and 
they  began  to  launch  into  the  water  sticks 
of  wood,  and  poles,  and  little  logs,  and  other 
such  floating  substances  as  they  could  find 
around  there,  and  then  they  amused  them- 
selves in  watching  them  as  they  were  borne, 
swiftly  away  down  the  stream ;  sometimes 
dashing  first  against  one  bank,  and  then 
against  the  other,  sometimes  shooting  straight 
forward  along  the  middle  of  the  current,  and 
now  and  then  plunging  headlong  down  a 
cataract,  or  a  cascade. 

In  this  sport  they  followed  the  stream 
down  for  some  distance,  until  Nathan  called 
out  to  them  not  to  leave  him  so  far  behind ; 


SO  THE  BOYS  LEFT  NATHAN  IN  THE  "WAGON.— Pago  160. 


MOMENTUM.  16 1 

and  then  they  went  back  to  him,  and,  after 
about  an  hour,  returned  home. 

The  next  day,  Hollo  came  again  to  look 
at  the  brook;  and  he  found  that  the  water 
had  subsided  nearly  to  its  accustomed  level. 
He  proceeded  immediately  to  the  site  of  the 
dam,  and  found  that  there  were  no  traces  of 
it  remaining  whatever ;  except  the  two  little 
cuts  in  the  mossy  bank  where  Jonas  had 
inserted  the  two  ends  of  the  board.  The 
water  was  meandering  slowly  along  the 
sandy  bed  of  the  brook,  taking  its  own  course 
unimpeded,  and  looking  as  if  it  was  saying 
to  Rollo,  '•'  Between  these  banks,  I  choose  to 
have  my  own  way." 

About  a  month  after  this,  as  James  and 
Rollo  were  at  work  among  the  bushes,  at  a 
considerable  distance  below  where  the  dam 
had  been  built,  James  suddenly  stopped 
cutting,  and  said,  with  a  loud  sigh,  — 

"  0  dear  me  !  I  am  tired.  I  wish  I  had 
a  good  place  to  sit  down." 

"Well,"  said  Rollo,  "we'll  look  about  and 
find  a  log  or  something.  0,  here  is  a  board 
waning  up  against  these  bushes." 

He  and  James  went  to  get  the  board,  and. 
io  their  utter  astonishment,  they  found  that 
g*  14* 


102  WATER. 

it  was  the  identical  board  which  Jonas  had  pu 
into  the  dam.  They  knew  it  by  the  plugs 
and  holes.  They  got  it  out  from  the  place  in 
the  bushes  where  it  had  been  caught,  and  made 
a  seat  of  it ;  and  this  was  the  end  of  their 
dam.  As  for  the  stakes  and  the  narrow  board, 
they  never  saw  any  thing  of  them  again. 
Thus  their  dam  was  first  undermined  by 
the  pressure  of  the  water  in  the  brook,  and 
then  afterwards  carried  wholly  away  by  its 
momentum. 


QUESTIONS. 

What  effect  did  Hollo  expect  would  be  produced  by  the 
rain,  and  the  consequent  rising  of  the  water,  in  the  brook  ? 
Which  would  the  force  of  the  jet  really  depend  upon,  the 
quantity  of  water  flowing  in  the  brook,  or  the  height  of  the 
water  above  the  dam  ?  What  were  the  appearances  of 
the  brook  when  Rollo  first  went  down  ?  When  he  went 
down  the  second  time,  did  he  expect  to  find  the  water 
higher,  or  not  so  high  ?  Why  did  he  expect  to  find  it  not 
BO  high  ?  How  was  it,  in  fact  ?  Why  was  it  higher  after 
the  rain  was  over  ?  What  was  the  appearance  at  the  dam  ? 
Was  the  board  carried  away  by  the  pressure  or  by  the  mo- 
mentum of  the  water  ?  What  is  momentum  f  Relate  tha 
circumstances  under  which  they  found  the  board 


CHAPTER    XI. 

JONAS'S    LECTUKE. 

ONE  day,  Rollo  and  Jonas  were  sent  away 
by  Hollo's  father,  about  eight  miles,  into  a 
neighboring  town,  in  a  wagon,  to  get  some 
apples  of  a  particular  ^kind,  called  the  Cherry 
Reds,  from  their  color.  They  bought  them 
of  a  farmer.  They  went  early  in  the  day, 
because  they  had  to  gather  the  apples  them- 
selves from  the  trees.  Jonas  and  Rollo  had 
to  climb  up  into  the  trees,  with  baskets,  and 
take  off  the  apples,  one  by  one,  to  prevent 
their  being  bruised ;  for  Rollo's  father  wanted 
to  keep  them  all  winter. 

About  four  o'clock,  they  had  finished 
gathering  the  apples.  They  put  them  into 
three  great  bags,  which  they  put  into  the 
wagon  behind  the  seat.  They  put  in  some 
straw  first,  to  prevent  the  apples  getting 
bruised  by  the  jolting  of  the  wagon.  Rollo 
tu:>k  two  apples  for  himself,  to  eat  by  the 
way,  and  so  they  set  out  for  home. 


1 64  WATER. 

They  went  on  very  prosperously  for  some 
time ;  but;  at  length,  when  they  were  stiL 
about  five  miles  from  home,  down  came  the 
back  of  the  wagon  to  the  ground,  with  a 
violent  shock. 

"  What's  the  matter  now  ? "  said  Rollo. 

"We've  broke  down,"  said  Jonas,  "some- 
how or  other." 

Rollo  jumped  out,  and  Jonas  soon  followed 
him.  They  found,  on  examination,  that  the 
hind  axletree  had  broken  short  off,  close  to  the 
wheel,  and  the  wheel  was  lying  down  flat  in 
the  road,  with  the  corner  of  the  wagon  rest- 
ing upon  the  centre  of  it. 

"And  what  shall  we  do  now?  "  said  Rollo. 

"  Why,  you  and  I  have  got  to  walk  five 
miles  home  ;  that's  all,"  said  Jonas. 

"Five  miles!  "said  Rollo;  "well,  I  can 
walk  five  miles." 

"  Yes,"  said  Jonas,  "  I  think  it  likely 
you  can  ;  though  you'll  get  pretty  tired." 

So  saying,  Jonas  went  into  the  woods  by 
the  side  of  the  road,  and,  with  a  hatchet, 
which  he  always  took  with  him  in  the 
wagon,  to  be  ready  in  case  of  an  accident,  he 
cut  a  long  and  stout  pole.  This  he  brought 
to  the  road,  and  put  it  underneath  the  wagon, 


JONAS'S    LECTURE.  167 

resting  one  end  of  it  upon  the  forward  axle- 
tree,  and  letting  the  other  end  trail  along 
upon  the  ground,  behind.  He  then  lifted  up 
the  back  part  of  the  wagon,  while  Rollo 
swung  the  end  of  the  pole  round  under  it,  in 
such  a  way  that  the  corner  of  the  wagon, 
which  had  lost  its  wheel,  rested  upon  the 
middle  of  the  pole. 

"  There,"  said  Jonas,  "  I  think  the  cherry 
reds  will  ride  now,  and  you  and  I  must  walk." 

So  he  hung  the  end  of  the  long  reins  over 
the  seat  of  the  wagon,  for  the  horse  was  very 
gentle  and  steady,  and  would  walk  along 
quietly  in  the  road ;  and  he  and  Rollo  fol- 
lowed behind. 

"  We  shall  be  late  home,"  said  Rollo. 

"  Yes,"  said  Jonas,  "  this  will  detain  us  an 
hour.  They  were  to  expect  us  about  six, 
and  it  will  be  seven  before  we  get  home. 
It  is  rather  bad  to  be  cast  away,  but  not 
quite  so  bad  to  be  cast  away  on  land  as  it  is 
at  sea." 

"Were  you  ever  cast  away,  Jonas,"  said 
Rollo,  "when  you  used  to  go  to  sea?  " 

"  No,"  said  Jonas  j  "I  did  not  go  to  sea  a 
great  while." 

"Speaking  of  going  to  sea,  Jonas,"  said 


168  WATER, 

Hollo,  "  makes  me  think  of  water,  and  ot  the 
lecture  which  you  promised  to  give  us.  1 
wish  you  would  give  it  now." 

"Yes,"  said  Jonas,  "I  promised  that,  if 
you  would  get  James  to  come  down  to  the 
dam,  I  would  give  you  a  lecture ;  but  this 
does  not  seem  to  be  a  very  good  occasion.  I 
can't  lecture  very  well  without  either  the 
apparatus  or  an  audience." 

"I  am  very  sorry  our  dam  was  carried 
away,"  said  Rollo ;  "  for  we  might  have  built 
it  up  higher,  and  so  had  it  flow  over  a  great 
deal  of  land,  and  make  a  pond ;  and  then  we 
might  have  sailed  on  it,  in  a  boat." 

"  If  you  only  had  a  boat  to  sail  in,"  said 
Jonas. 

"We  could  have  got  a  box;  a  long  box 
would  do.  It  is  not  necessary  —  is  it  ?  —  to 
have  the  end  sharp?  " 

"  No,"  said  Jonas ;  "  but  a  box  would  not 
be  tight  enough." 

"  Couldn't  I  sail  a  little  in  a  tub  ? "  said 
Rollo. 

"  A  tub  would  be  tight,  at  any  rate,"  said 
lonas. 

'•'  And  wouldn't  it  bear  me  up  ?  " 

"  Yes,"  said  Jonas. 


JONAS'S    LECTUKE.  169 

"  Did  you  ever  see  any  body  sail  in  a  tub  ? " 
asked  Rollo. 

"No,"  replied  Jonas,  "I  never  did." 

"  Then  you  mean."  added  Rollo,  "  that 
you  think  it  would  bear  me  up." 

"  No,"  said  Jonas,  "  I  am  sure  it  would." 

"  But  how  can  you  be  sure,"  said  Rollo, 
"  unless  you  have  seen  it  tried  ?  " 

"  Because,"  said  Jonas,  "  I  know  the  prin- 
ciple that  it  depends  upon." 

"  What  is  the  principle  ? "  said  Rollo. 

"  The  principle  is,"  said  Jonas,  "  that,  if 
any  thing  is  floating  in  the  water,  it  sinks 
into  it  low  enough  to  displace  its  own  weight 
of  water." 

"I  don't  understand  you  very  well,"  said 
Rollo. 

"  Well,"  said  Jonas,  "  I  can  explain  it 
better  by  taking  a  particular  thing. 

"  We  will  suppose,"  he  continued,  "  that 
there  is  a  log  of  wood  floating  in  the  water. 
As  far  as  it  sinks  down,  it  displaces  the  water ; 
that  is,  it  crowds  it  away." 

"  Yes,"  said  Rollo. 

"  And  it  makes  a  kind  of  depression,  or  pit, 
in  the  water." 
A  15 


170  WATER. 

"  I  don't  exactly  understand  that/5  said 
Rollo. 

"  Why,  suppose  the  water  were  to  freeze 
all  around  the  log,  and  then  you  were  to 
take  the  log  out." 

"  You  could  not  get  it  out ;  it  would 
stick,"  interrupted  Rollo. 

"  Why,  the  sun  might  shine  upon  the  log, 
and  warm  it,"  said  Jonas,  "  and  so  melt  the  ice 
that  touched  it,  a  little,  and  thus  loosen  it ; 
—  or,  at  any  rate,  we  may  suppose  the  log 
taken  up.  Now,  do  you  not  see  that  there 
would  be  a  kind  of  a  pit,  or  depression,  in  the 
ice,  where  the  log  had  been  ?  " 

"Yes,"  said  Rollo,  "just  of  the  shape  of 
the  log." 

"No,"  said  Jonas,  "but  just  of  the  shape 
of  that  part  of  the  log  which  was  under 
water." 

"  Yes,"  said  Rollo,  "  that  is  what  I  mean." 

"Well,"  said  Jonas,  "now  suppose  we 
trere  to  fill  up  this  pit,  or  depression,  in  the 
ice,  with  water  again,  exactly  full,  —  then 
the  log  will  weigh  just  as  much  as  the  water 
poured  in  to  fill  the  depression,  which  the 
log  made  by  floating.  That's  the  principle." 


JONAS'S    LECTURE.  171 

"But  some  logs  would  be  heavier  than 
others,"  said  Hollo. 

"Then  they  will  settle  down  just  so 
much  the  deeper.  Everything  that  floats, 
will  always  settle  down  into  the  water  until 
the  cavity  that  it  makes  will  hold  just 
enough  water,  to  weigh  as  much  as  the  thing 
does  itself." 

"  That's  rather  curious,"  said  Hollo. 

"  Yes,"  said  Jonas,  "  it  is.  And  you  might 
try  the  experiment  some  time  in  this  way. 
Take  a  bowl,  and  fill  it  full  of  water,  — 
exactly  full.  Then  put  it  into  a  basin  which 
has  no  water  in  it.  Then  put  a  block  of 
wood  very  gently  down  into  the  water  of  the 
bowl." 

"  That  will  spill  it  over,"  said  Hollo. 

''Yes,"  said  Jonas,  "the  bowl  was  full 
before,  and  of  course  some  will  go  over ;  but 
it  will  be  caught  in  the  basin.  Now,  you 
see  that  what  is  spilt  over  will  be  just  as 
much  in  bulk  as  the  part  of  the  block  which 
is  under  water." 

"  In  bulk  ?  what  do  you  mean  by  that  ?  " 
asked  Rollo. 

"  Why,   in   size :    there   will   be  just   as 


172  WATER. 

mu^h  in  quantity;  for  the  bowl  is  as  fuh 
after  the  block  is  put  in  as  before,  excepting 
the  room  taken  up  by  the  part  of  the  block 
which  is  under  water.  Of  course  what  is 
spilt  over  will  be  just  as  much  in  bulk  as 
that  part  of  the  block." 

"  Well,"  said  Rollo. 

"  Well,  then,"  said  Jonas,  "  if  you  weigh 
this  water,  which  is  spilt  over  by  putting  in 
the  block,  you  will  find  that  it  will  weigh 
just  as  much  as  the  whole  block  does." 

"  Exactly  ?  "  asked  Rollo. 

"  Yes,  exactly,  if  you  perform  the  experi- 
ment carefully." 

"  How  did  you  know  ? "  asked  Rollo. 

"  I  read  it  in  a  book  which  your  father 
lent  me,"  said  Jonas.  It  said  in  that  book 
that  a  floating  body  displaces  its  own  weight 
of  water.  I  could  not  understand  it  for  a 
long  time.  I  did  not  know  exactly  what 
was  meant  by  displaces." 

"  And  what  does  it  mean  ?  "  said  Rollo. 

"  Why,  moves  it  away  when  it  sinks  down 
in  it.  A  ship,  for  instance,  settles  down  into 
the  water  until  it  makes  a  depression  big 
enough  to  hold  just  as  much  water  as  the 


JONAS'S    LECTURE.  173 

fehip  weighs ;  —  masts,  sails,  rigging,  cargo, 
and  all;  and  when  it  has  settled  down  as 
far  as  that,  it  will  not  go  any  farther." 

"  Why  not  ?  "  asked  Hollo. 

"Because,"  said  Jonas,  "then  it  presses 
just  as  heavy  on  the  water  under  it  as  the 
water  would,  which  was  before  in  the  place 
where  it  floats ;  and  so  all  will  be  at  rest,  just 
as  before.  If  the  ship  were  to  press  any 
heavier  upon  the  water  under  it,  than  the 
water  would  which  would  be  enough  to  fill 
up  the  depression  which  it  makes,  then  it 
would  sink  a  little  deeper.  And  if  it  did  not 
press  quite  so  heavy,  then  the  water  under  it 
would  buoy  it  up  a  little  higher.  Because, 
you  see,  the  water  under  the  ship  will  only 
be  at  rest  when  the  ship  presses  just  as  heav- 
ily upon  it,  as  the  water  did  that  was  in  the 
cavity  which  the  ship  makes,  before  the  ship 
came  there." 

Perhaps  Hollo  did  not  understand  the  last 
part  of  Jonas's  explanation ;  for  just  at  the 
time  he  was  making  it,  Hollo  saw  a  chaise 
coming  along  the  road,  some  distance  before 
them. 

"Jonas,"  said  he,  "here  comes  a  chaise, 
\ve  must  turn  out." 
15* 


174  WATER. 

But  just  as  Jonas  was  going  to  take  hold 
of  the  reins  to  be  ready  to  turn  the  horse  out 
of  the  road,  the  chaise  itself  turned  down 
another  road,  and  so  saved  them  the  trouble. 

So  Jonas  came  back  behind  the  wagon 
again,  and  Hollo  asked  him  to  go  on  with 
his  explanations. 

"  Well,  then,  it  follows  from  what  I  told 
you,"  said  Jonas,  "  that  if  any  kind  of  wood 
is  just  half  as  heavy  as  water,  then  it  will 
have  to  sink  down  until  it  is  just  one  half 
under  water;  for  then  it  will  have  dis- 
placed just  water  enough  to  be  equal  to  it  in 
weight.  If  it  is  very  light,  like  cork,  then  it 
will  not  sink  down  so  far :  my  book  said  that 
cork  was  about  a  quarter  as  heavy  as  water  ; 
and  so,  when  it  floats,  one  quarter  of  it  would 
be  under  water  and  three  quarters  above." 

"  Suppose  anything  was  just  exactly  as 
heavy  as  water,"  said  Hollo. 

"  Then,"  said  Jonas,  "  it  would  sink  until 
the  top  of  it  was  just  level  with  the  surface 
of  the  water." 

"  Is  there  anything  just  as  heavy  as  the 
water  ?  "  asked  Hollo. 

"Yes,"  replied  Jonas,  "  you  are." 

"  I  am  ?  "  said  Hollo. 


JONAS'S    LECTURE.  175 

"Yes,"  replied  Jonas  ;  "  that  is,  your  body 
is  very  nearly  as  heavy  as  a  mass  of  water 
of  the  same  bulk." 

"  Then,  if  I  was  to  get  into  the  water,  I 
should  sink  in,  just  level  with  the  top  of  the 
water." 

"Yes,"  said  Jonas,  "very  nearly." 

"  Then  it  is  not  exact,"  said  Rollo ; 
"  would  it  be  a  little  more  or  a  little  less  ?  " 

"  Why,  it  would  depend  upon  the  state  of 
your  breath,"  said  Jonas ;  "  sometimes  a  little 
more,  and  sometimes  a  little  less." 

"  Why,  Jonas !  "  said  Rollo ;  "  how  can 
that  be  ? " 

"  If  you  draw  a  long,  full  breath,"  said  Jo- 
nas, "  so,"  (and  here  Jonas  paused  a  moment, 
and  stood  still  in  the  road,  and  made  a  long 
and  full  inspiration,  that  is,  drawing  in  of  the 
breath ;)  "  if  you  do  so,  the  air  goes  into  your 
lungs,  and  swells  out  your  chest,  and  makes 
you  larger  and  lighter.  But  if  you  breathe 
out  as  much  of  the  air  as  you  can,"  (and  here 
Jonas  paused  again,  and  made  a  long  expira- 
tion,} "then,"  he  added,  resuming  his  breath 
again,  "  the  lungs  are  exhausted,  the  chest 
shrinks,  and  the  body  becomes  heavier." 


176  WATER. 

"  I  shouldn't  think  that  would  make  much 
difference,"  said  Rollo. 

"  Yes,"  said  Jonas,  "  it  makes  a  great  deal 
of  difference.  When  a  boy  is  in  the  water. 
if  he  draws  in  as  much  breath  as  he  can  into 
his  lungs,  he  floats.  If  he  breathes  out  all 
the  air  he  can,  he  sinks." 

"  Did  you  ever  try  it  ?  "  said  Rollo. 

"Yes,"  said  Jonas,  "very  often,  when  I 
have  been  in  the  water." 

"Then  the  body  itself,"  said  Rollo,  "is 
just  about  as  heavy  as  water." 

"  Yes,"  said  Jonas,  "  I  believe  it  is  — just 
about." 

"And  then,"  added  Rollo,  "it  will  sink 
just  even  with  the  water." 

"  Yes,"  said  Jonas,  "  it  must  sink  until  it 
takes  the  place  of  its  own  weight  of  water ; 
and  its  own  weight  of  water  would  be  just 
as  big  as  it  is  itself.  So  it  must  sink  until  it 
is  just  all  in." 

"That's  the  principle  then,  is  it?"  said 
Rollo. 

"  Yes,"  said  Jonas,  "  that's  the  principle." 

"  I  don't  see,"  said  Rollo,  "  how  you  can 
tell  by  it  whether  a  tub  would  bear  me  up, 
or  not." 


JONAS'S    LECTURE.  177 

"  Why,  it  shows  how  much  the  tub  must 
sink,  if  you  get  into  it,"  said  Jonas. 

"  How  ? "  asked  Rollo. 

"  Why,  the  tub  must  sink  just  as  much 
deeper  than  it  did  before  you  got  into  it,  as 
to  be  equal  to  the  size  of  your  body.  Because 
you  see,  that  whether  you  are  in  a  tub,  or 
out  of  it,  in  order  to  be  buoyed  up  in  the 
water,  you  must  take  the  place  of  as  much 
water  as  will  weigh  just  as  much  as  you  do 
yourself ;  and  as  water  is  just  about  as  heavy 
as  your  body  is,  you  must  take  the  place  of 
a  quantity  of  water  just  as  big  in  bulk.  Now, 
don't  you  tliink  a  tub  is  bigger  than  you 
are?" 

"  Yes,"  said  Rollo,  "  it  is  bigger  round, 
but  then  it  is  not  so  high." 

"No,"  said  Jonas,  "  it  is  not  so  high,  and 
it  is  very  different  in  shape ;  but,  making  al- 
lowance for  the  difference  of  shape,  don't 
you  think  that,  on  the  whole,  it  is  a  great 
deal  bigger  than  you  are  ? 

"That  is,"  continued  Jonas,  "suppose 
there  was  a  wax  figure,  just  as  big  as  you 
are,  and  this  wax  figure  was  to  be  melted 
down,  and  the  wax  poured  into  the  tub  do 
you  think  it  would  fill  it  full  ? ' 


178  WATER. 

"No,"  said  Rollo,  "I  don't  think  it 
would." 

"I'm  sure  it  would  not,"  said  Jonas. 
"  Now,  if  your  body  would  fill  the  tub  half 
full,  if  put  into  it  compactly,  then  it  would 
sink  the  tub  half  down  into  the  water.  If 
you  were  equal  in  size  to  two  thirds  the  tub 
full,  then  the  tub  would  sink  two  thirds  its 
depth  into  the  water." 

"And  it  is  just  so  with  a  boat,  I  suppose," 
said  Rollo. 

"  Yes,"  said  Jonas  ;  "  when  a  man  steps 
into  a  boat,  he  sinks  it  into  the  water,  just 
enough  more  than  it  was  before  to  be  equal 
to  the  size  of  his  own  body.  Of  course,  if  it 
is  a  large  boat,  it  would  not  have  to  sink  so 
far  as  if  it  was  small." 

"  And  if  it  was  a  great  ship,  it  would  not 
sink  any." 

"  Yes  it  would,"  said  Jonas. 

"No,  it  would  not,"  said  Rollo,  "I  know." 

"  How  do  you  know  ?  "  asked  Jonas. 

"  Why,  once  I  went  into  a  ship,  and  it  did 
not  move  at  all  when  I  stepped  on  it." 

"  How  did  you  know  ?  "  said  Jonas. 

"  Why,  I  should  have  felt  it  sinking  under 
rue  a  little,  if  it  had  sunk  any." 


JONAS'S    LECTURE.  179 

"  Suppose  that  another  boy  had  gone  aboard 
the  ship  just  after  you  did;  would  it  have 
sunk  any  under  him?  " 

"No,"  said  Rollo.  "There  was  another 
boy,  James ;  and  it  did  not  sink  at  all." 

"  Suppose  there  had  been  fifty  or  one  hun- 
dred boys,"  said  Jonas. 

"  O,  if  there  were  a  great  many,"  said 
Rollo,  "  I  suppose  that  after  a  while  the  ship 
would  begin  to  sink." 

"  Then  you  think  that  some  boys  might 
go  aboard  a  ship,  without  making  it  settle  any 
in  the  water,  but  that  other  boys  would  make 
it  settle." 

"No,"  said  Rollo,  "I  do  not  mean  that 
some  would  make  it  settle,  and  others  would 
not,  but  that,  when  there  were  a  great  many, 
all  together  would  make  it  settle." 

"  Yes  ;  but,"  said  Jonas,  "  they  would  not 
all  go  aboard  together.  I  mean  to  suppose 
that  they  come  one  after  another;  and  of 
course,  if  it  does  not  settle  any  at  first,  but 
afterwards  does  settle,  there  must  be  some 
one  boy,  whose  coming  aboard  first  makes 
it  sink  deeper  into  the  water." 

Rollo  did  not  answer.  He  did  not  know 
exactly  what  to  say  to  Jonas's  reasoning. 


180  WATER. 

"Now,"  said  Jonas,  "it  is  very  clear  that, 
if  a  thousand  boys  coming  aboard  a  ship, 
would  make  it  settle  at  all  deeper  into  the 
water,  then  one  boy  must  make  it  settle  one 
thousandth  part  as  much." 

"  Well,"  said  Hollo,  "  if  you  do  make  it 
out  so  in  reasoning,  I  know  it  is  not  so  ;  for  I 
have  tried  it." 

"  You  are  a  very  fine  philosopher,"  said 
Jonas ;  and  he  began  playfully  to  punch 
Hollo  with  the  butt  of  his  whip  handle. 
"  You  believe  your  senses  rather  than  youi 
reason !  A  fine  philosopher  you !  " 

Hollo  leaped  over  the  end  of  the  pole, 
which  supported  the  end  of  the  wagon,  to 
get  out  of  Jonas's  way.  Jonas  pursued  him, 
pointing  the  end  of  his  whip  handle  towards 
him ;  and  Hollo,  with  shouts  of  laughter, 
sprang  across  to  a  grassy  bank  by  the  side  of 
the  road,  and  ran  up  among  some  bushes, 
where  Jonas  could  not  reach  him.  Every 
time  he  drew  near  the  road  a  little,  Jonas 
pointed  his  whip  handle  towards  him  in  a 
menacing  manner,  and  so  kept  Hollo  from 
returning. 

Hollo  ran  along  upon  the  bank  thus,  foi 
some  time. 


JONAS'S    LECTURE.  18*. 


QUESTIONS. 

On  what  expedition  were  Jonas  and  Rollo  sent  ?  What 
tccident  happened  to  them  when  coming  home  ?  What 
part  of  the  wagon  was  broken  ?  How  did  Jonas  remedy 
the  difficulty  ?  What  was  the  supposition  which  Jonas 
made  respecting  the  log  of  wood  floating  in  the  water ? 
What  is  meant  by  displacing  f  How  much  water  did 
Jonas  say  that  the  log  of  wood  would  displace  ?  How  did 
Jonas  prove  that  the  log  would  settle  down  into  the  water 
until  it  had  displaced  its  own  weight  of  water  ?  What  ex- 
periment did  Jonas  describe  to  be  performed  with  a  bowl 
full  of  water  ?  What  is  the  meaning  of  bulk?  What  did 
Jonas  teach  Rollo  respecting  the  weight  of  the  human 
body  compared  with  water  ?  How  did  he  say  it  depended 
upon  the  state  of  the  breath?  How  did  he  calculate 
whether  a  tub  would  be  sufficient  to  buoy  Rollo  up? 
What  is  the  rule  in  regard  to  the  depth  of  water  which  a 
ship  will  draw?  Would  Rollo's  going  on  board  a  ship 
make  it  sink  any  deeper  into  the  water  ?  Why  did  Jonaa 
think  it  would  ?  Why  did  Rollo  think  it  would  not ? 
16 


CHAPTER    XII. 

DISCRETIONARY   POWER. 

ROLLO  soon  began  to  be  tired  of  the  baiik, 
and  wanted  to  return  to  the  road  again. 
The  smile  faded  away  from  his  countenance, 
and  a  serious  and  almost  a  displeased  expres- 
sion took  its  place. 

"  Now,  Jonas,"  said  he,  "  you  are  not 
fair  ;  making  mo  run  out  of  the  road  so  fast, 
and  then  keeping  me  in  this  rough  place.  I 
shall  use  up  all  my  strength,  and  not  have 
any  left  to  get  home  with." 

"  So  you  will,"  said  Jonas ;  "  when  we 
are  on  a  forced  march,  we  must  not  waste 
any  of  our  strength  in  play.  So  come  back, 
and  I  will  not  trouble  you  any  more." 

"And  I  think,"  continued  Hollo,  "that 
you  ought  to  let  me  ride  a  little  way,  to  pay 
for  giving  me  such  a  run." 

"  Well,"  said  Jonas,  "jump  in  here  behind, 
and  ride  on  the  bags." 

So  Hollo  caught  hold  of  the  back  of  the 


DISCRETIONARY     POWER.  183 

wagon,  and,  putting  his  foot  upon  the  pole, 
where  it  came  out  from  underneath,  he 
climbed  in.  Jonas  helped  him.  a  little. 

"  Sit  over  towards  the  wheel,"  said  Jonas. 

"  Why  ?  "  said  Rollo. 

"  Because,"  said  Jonas,  "  if  you  sit  neai 
the  pole,  your  weight  comes  upon  the  pole, 
and  makes  it  drag  harder  upon  the  ground.' 

So  Rollo  sat  over  towards  the  wheel,  which 
remained  in  its  .place.  The  wheel  which 
came  off,  the  boys  had  put  in  before  the  seat, 
so  that  it  was  out  of  the  way. 

Rollo  rode  here  for  some  time.  At  length 
he  said,  — 

"  Jonas,  would  this  wagon  be  large  enough 
to  float  me,  if  it  was  in  the  water  for  a 
boat  ? " 

"  Yes,"  said  Jonas,  "no  doubt."" 

"  Because,"  said  Rollo,  "  it  will  hold  more 
than  what  would  be  equal  to  my  bigness." 

"Yes,"  said  Jonas,  "that  is  the  way  to 
judge ;  only  we  must  make  allowance  for 
what  it  would  sink  in,  of  its  own  accord.  If 
the  wagon  body  were  to  be  taken  off  the 
wheels,  and  put  into  the  water,  it  would  sink 
itself  down  into  the  water  a  little  way,  be- 


1 84  WATER. 

cause  it  is  made  of  a  solid  kind  of  wood,  and 
has  considerable  iron  in  it.  Then,  after  that, 
it  would  sink  only  enough  more,  if  you  were 
to  get  into  it,  to  amount  to  just  the  bigness 
of  your  body,  under  water ;  and  that  would 
be  only  a  very  little  way;  for  the  wagon 
body  is  so  long  and  broad,  that  it  would 
have  to  sink  only  a  very  little  way,  to  dis- 
place as  much  water  as  would  equal  the 
bigness  of  your  body." 

"  Not  more  than  an  inch  ?  "  said  Rollo. 

"  Very  likely,"  said  Jonas.  "  I  think  it 
very  probable  that  an  inch,  or  two  inches,  all 
over  the  bottom  of  the  wagon,  would  be  as 
much  in  bulk  as  the  whole  of  your  body. 
They  always  make  ferry-boats,  which  are  to 
be  used  for  carriages  and  loaded  teams,  broad 
and  flat.  so.  that,  when  the  teams  are  in,  they 
may  not  draw  much  water." 

"  Draw  much  water  ?  "  replied  Rollo  ; 
"  what  do  you  mean  by  that  ?  " 

"  Why,  sink  down  deep  into  the  water," 
said  Jonas.  "If  a  boat  or  a  vessel  sinks 
down  twenty-four  inches  into  the  water,  they 
say  she  draws  twenty-four  inches.  Loaded 
vessels  draw  ten  or  twelve  feet." 


DISCRETIONARY     POWER.  185 

"  I  don't  see  what  they  call  it  draw,  for." 
laid  Rollo. 

"  Nor  I,"  said  Jonas ; '"  only  I  know  they 
do  call  it  so.  It  is  very  important  to  know 
how  much  a  vessel  draws." 

«  Why  ?  "  said  Rollo. 

"  Because  then  they  know  how  deep  water 
she  must  have  to  float  in.  I  read  in  a  news- 
paper yesterday,  that  there  was  a  bar  at  the 
mouth  of  some  harbor  or  other,  so  that 
vessels  drawing  over  eight  feet  of  water 
couldn't  get  in  at  low  tide.  But  ferry-boats 
are  made  broad  and  flat,  so  that  they  only 
draw  a  few  inches." 

11  Why  don't  they  make  the  ships  broad 
and  flat?  "  said  Rollo ;  "  and  then  they  could 
go  over  all  the  bars." 

"Because  they  would  not  sail  well,"  re- 
plied Jonas.  "  They'd  go  very  slow,  and 
the  contrary  winds  would  drive  them  all 
about  the  ocean." 

"I  remember  that  ferry-boats  are  flat," 
said  Rollo.  "I  went  over  one  once  in  a 
chaise.  I  was  riding  with  my  father." 

"And  did  the  ferry-boat  sink  in  very 
deep?" 

i*  16* 


186  WATER. 

"No,  not  very.  I  thought  it  would  sink 
very  deep,  it  was  such  a  low  boat.  I  was 
afraid  to  have  father  drive  in.  I  wanted  to 
get  out  of  the  chaise,  but  my  father  said 
there  was  no  danger.  But,  Jonas,  why  don't 
they  have  ferry-boats  shaped  like  ships  ?  anrt 
ihen  we  could  sail  across  the  river  faster." 

"Yes,  perhaps  the  boat  might,  sail  faster 
where  the  water  was  deep ;  but  then  it 
would  be  constantly  getting  aground  on  the 
shallows,  and  it  could  not  come  near  the 
shore ;  and  so  they  have  to  make  ferry- 
boats flat-bottomed  and  broad." 

"But,"  said  Hollo,  "  I  have  seen  vessels, 
sailing  in  rivers,  which  were  shaped  just  like 
ships." 

"Yes,"  said  Jonas,  "vessels  that  sail  up 
and  down  rivers  may  be  built  like  ships,  be- 
cause they  can  keep  in  the  channel,  where 
the  water  is  deep.  But  ferry-boats  have  to 
go  back  and  forth,  across,  and  of  course  have 
to  go  over  shallow  water,  as  well  as  deep ; 
and  so  they  have  to  build  them  broad  and  Hat 
in  order  that  they  may  not  draw  much  water. 
But  whatever  the  shape  of  the  bottom  of 
Ihe  boat  is.  when  the  loading  is  put  in,  it 


DISCRETIONARY     POWER.  187 

will  always  make  it  settle  down  till  it  has 
crowded  away  just  as  much  water  as  it 
weighs  itself." 

"  Yes,"  said  Rollo. 

"  And  in  the  case  of  a  man  or  a  boy,  you 
see,"  continued  Jonas,  "  as  they  are  just  as 
heavy  as  water,  they  will  settle  down  the 
boat  till  it  has  crowded  away  just  as  much 
water  in  bulk,  as  will  equal  the  size  of  their 
bodies." 

By  this  time,  Rollo  began  to  be  somewhat 
tired,  and  he  asked  Jonas  how  much  farther 
they  had  got  to  go.  Jonas  said  it  was  about 
two  miles 

"  I  am  sorry  that  our  wagon  got  broken, 
Jonas,"  said  he.  "  Shall  you  be  able  to 
mend  it  ?  " 

"  No,"  said  Jonas,  "  it  needs  a  new  axle- 
tree." 

"  And  can't  you  make  an  axletree  ? "  said 
Rollo. 

"  No,"  replied  Jonas,  "  not  for  a  wagon  ; 
L'ough  I  could  make  one  for  a  cart." 

"  What  will  father  do,  then  ?  "  said  Rollo. 

"  He  will  send  it  to  the  wagon-maker's,  1 
suppose,"  said  Jonas. 


188  WATER. 

"  Where  does  the  wagon-maker  live  ?  " 
asked  Hollo. 

"  Why,  he  lives  on  this  very  road,"  replied 
Jonas ;  "  we  shall  go  directly  by  his  shop." 

"  Then  why  can't  you  leave  the  wag  or 
there  when  you  go  by  ?  "  said  Rollo. 

"  That  is  a  question,  indeed,"  replied 
Jonas ;  "I  had  not  thought  of  that  plan. 
But  I  have  no  authority  to  leave  the  wagon." 

"  No  authority  ? "  repeated  Rollo. 

"  No,"  said  Jonas ;  "  my  orders  were  to  go 
and  get  some  apples,  and  bring  them  home ; 
aud  I  have  nothing  to  do  but  to  obey  the 
orders." 

"  But  then  father  will  only  have  to  send 
the  wagon  right  back  again  over  the  same 
ground  to-morrow  morning." 

"  Yes,"  said  Jonas,  "  if  he  concludes  to 
have  it  mended  to-morrow,  and  also  if  he 
concludes  to  employ  this  man  to  do  it.  I 
presume  he  will ;  and  if  I  had  discretionary 
power,  to  act  as  I  thought  best,  I  should 
leave  it ;  but  when  no  discretionary  power 
is  given,  then  the  only  way  is  to  obey 
orders.  That's  the  rule  at  sea,  and  it  ought 
to  be  the  rule  on  land." 


niSCRETIONARY     POWER.  169 

"  Yes,  but,  Jonas,  you  told  me  once  your- 
self/' rejoined  Hollo,  "  that  you  always  had 
discretionary  power  in  emergencies ;  you 
said  that  it  was  understood  and  implied  be- 
tween you  and  father,  that  when  anything 
unexpected  occurred,  you  were  to  act  accord- 
ing to  your  best  discretion."  ' 

"  Did  I  ?  "  said  Jonas. 

"  Yes,"  said  Hollo,  positively. 

"  Well,"  said  Jonas,  "  I  suppose  I  have 
some  discretionary  power;  but  that's  a 
kind  of  power  which  it  is  rather  dangerous 
to  use." 

Here  the  conversation  stopped,  and  the 
boys  walked  along  for  some  time  in  silence. 
They  were  both  weary  with  walking,  and 
felt,  on  that  account,  less  inclined  to  talk. 
After  some  time,  Rollo  said,  — 

"  Well,  Jonas,  what  do  you  think,  on  the 
whole,  that  you  shall  do  about  the  discre- 
tionary power  ? " 

"  Why,  I  think,  on  the  whole,"  replied  Jo- 
nas, "  that  I  shall  take  the  responsibility  of 
using  it." 

"And  leave  the  wagon  at  the  wagon- 
maker's  ? " 


190  WATER. 

"Yes,"  said  Jonas,  "only  I  shall  leave 
such  directions  as  shall  make  it  perfectly 
safe." 

The  boys,  soon  after  this,  arrived  at  the 
wagon-maker's.  It  was  a  shop  near  a  mill, 
and  it  had  a  lathe  and  a  circular  saw,  which 
were  moved  by  water.  Rollo  went  down 
under  the  shop  with  Jonas,  to  see  the  water 
spouting  with  great  force  against  the  water- 
wheel. 

"  That  spouts  out  with  rather  more  force 
than  the  water  did  from  your  dam,"  said 
Jonas. 

"  Yes,  indeed,"  said  Rollo. 

"  That  is  because  there  is  a  greater  head 
of  water,"  said  Jonas. 

"  Yes,"  said  Rollo,  "  it  is  pressed  by  a 
higher  column.  I  wonder  how  high  it  is." 

When  they  went  up  into  the  shop  again, 
Jonas  asked  the  man,  and  he  said  that  they 
generally  had  about  six  feet  of  water.  When 
Rollo  heard  this,  he  was  not  surprised  that 
the  water  spouted  out  against  the  wheel 
with  so  much  force. 

Jonas  ascertained  from  the  wagon-maker 
how  much  it  would  cost  to  mend  the  wagon 


DISCRETIONARY     POWER.  191 

and  also  when  he  could  do  it.  He  then 
told  him  that  he  might  begin  to  mend  it  at 
nine  o'clock  the  next  morning,  unless  he 
heard  from  Hollo's  father  before  that  time. 
"  In  case  he  does  not  wish  to  have  it  mended." 
said  he,  "I  can  come  over  early,  and  let  you 
know." 

Then  Jonas  took  the  harness  off  the  horse, 
and  put  it  in  a  corner  of  the  shop.  He  bor- 
rowed a  piece  of  a  blanket  of  the  wagon- 
maker,  and  placed  it  across  the  horse's  back, 
and  then  he  put  Hollo  on.  Thus  Hollo  had 
a  ride  the  rest  of  the  way.  He  walked  the 
horse,  to  keep  in  Jonas's  company,  until  they 
had  got  within  about  half  a  mile  of  home  ; 
and  then  he  trotted  on,  to  tell  them  that 
Jonas  was  coming. 


QUESTIONS. 

When  Rollo  got  into  thf  wagon,  where  did  he  take  his 
neat,  at  first  ?  What  change  in  it  did  Jonas  propose  ?  For 
what  reason  ?  What  question  did  Rollo  ask  about  the 
wagon?  What  was  Jonas's  answer?  Why  did  he  think 
that  the  wagon  would  sink  but  a  little  way  with  Ro'.lo's 
weight  in  it  ?  What  did  he  say  about  the  construction  of 


192  WATER. 

ferry-boats  ?  What  is  meant  by  a  vessel's  drawing  six  feet 
of  water?  Why  are  not  ships  made  flat-bottomed,  like 
ferry-boats  ?  What  led  to  the  conversation  about  discre- 
tionary power f  Was  Jonas  reluctant  to  use  such  power! 
What  precautions  did  he  take  to  make  his  use  of  it  BB.le  ? 


EKD  OP   PART   X. 


* 


A    000653506    6 


